I invented this new alt for the reason of my anonymity.

You see, I've always wanted to try out CRP and casual roleplays, yet I cannot really do much to extend my posts. Does anyone have any tips and shit?

Interesting. So are your normal roleplays mainly just snippets of dialogue? The best way to extend your posts is to first find out what is missing or lacking.

I invented this new alt for the reason of my anonymity.

unless you're like one of the 10 people everyone knows on the site, all of which are most definitely not required of post extension, I don't think you need to worry too much about getting shit on for your identity lmao

To answer the actual question, though, there's only one way to "extend" your posts.

Practice, ask for feedback and discuss writing.

Think of "why" you need to extend your posts. Is it a lack of getting your core message across? Are you not doing enough? What is it that you do wrong?

For example, I constantly swing between barely two paragraphs and about 20 pages worth of exposé depending on the scenario I'm writing for. Frankly put, if I have nothing to write about, I won't be writing a lot. That's something you need to think about- how much material do you have to go over, and in what extent so the reader can understand the message you're trying to convey?

Let me write up like, an example for you real quick.

"Samantha sighed and released her grip on the locket. It fell into the puddle once more, creating a small splash that covered her shoes in little driblets of water. She didn't know what she was expecting; some revelation? A sudden epiphany that connected the threads of the mystery she'd been searching so long for? Ridiculous. She was no further than where she started. The man who dropped it could worry about the locket himself, Samantha was done with it. Crushed as she stepped over the small pendant, whatever photo was inside of it quickly got rendered undecipherable by the erosion from the rainwater seeping into its form. Only she and the original owner were privy to the knowledge contained inside."

As you can see, there's actually not a lot here. Character has a locket she drops into a puddle, a puddle it had apparently been in, and then steps on it as character continues on its way. The rest of the space I managed to fill up with her inner conflict and what said locket means to her, because that's what the main drive here was. If it wasn't, and the actions pertaining to character were the important bit, it'd read more like:

"Samantha dropped the locket she'd picked up once more into the puddle, then stepped on it to crush the pendant. The rainwater eroded the paper contents it held as she carelessly continued on her way."

As you can see, this is much shorter because the information I wish to convey you is purely the external happening without the internal monologue. Do not use internal monologue as a shorthand for artificially extending the length of any given post, though. It needs to have a purpose to be there. If I wanted more to happen in the scene, extending it as you will, without the monologue, I'd maybe do something like;

"Samantha dropped the locket she'd picked up once more into the puddle, then stepped on it to crush the pendant. The rainwater eroded the paper contents it held as she carelessly continued on her way. She entered the shopping district, devoid of life due to the cold temperature. Her head whipped around for a little while before she settled on her goal: The flower store. Samantha quickly paced over, opened the door and called out:

'Hey! I know you're there!'"

I'm going to stop giving examples now, but you get the point. There's a myriad of things you can do depending on which information you're wanting to convey to the reader. I haven't even delved into the why of what causes this character to do what she does. While not always needing a mention, it's another avenue you can explore.

All in all, though, don't forcefully extend something without meaning. Without your real alias to latch onto, I can't exactly tell what you're doing wrong, but I think I gave you a general enough idea of what you could do. Don't feel afraid to ask your peers what you can do better either and where to improve. A lot of things just comes down to becoming a better writer and putting in the effort to get to that point.

Then again I'm a total amateur that doesn't know what he's talking about so ᕕ( ᐛ )ᕗ

It's a shame you decided to use an alt, because I could look at a few of your posts and tell you exactly how you could make your posts longer. But here's some general "tips and shit"

-Write in more detail. Write exactly what the character is doing instead of a one word summary of the action. Don't just "mix a potion," explain how the potion is being made. Where did the herbs come from? what do they smell like? Did you need to boil any water for this? Is making potions a mundane skill or is it actually really hard?

-Write what your character is thinking. You have to be careful with this one. Some people have a tendency to write every mundane thought they have, but it's certainly welcome to see how a character makes a choice or a decision that doesn't normally side with the way they operate.

-Write the history of something, or a character's history of something. If your character finds themselves in familiar territory, write a brief description of why they know this place or how they know how a particular device works.

-Educate your readers. I'm constantly reading articles about things my characters are into so that I can better explain what they are doing or why things work a certain way. Your average reader probably doesn't know how a mountain climber ties off their equipment, that an alligator has a transparent third eyelid for hunting underwater, or that a blow fish's liver is the most poisonous organ in its body.

And as @Ammokkx already pointed out, there needs to be a reason for it. Nobody wants to read an empty post that was long for the sake of being long.

@BrokenPromise and @Ammokkx basically covered the gist of it, but one thing that can help is spending time reading the posts of writers you like and paying attention to the details they put in; do things like engage the senses, think of body language or how a character would physically do an action; are they hurt or tired? What's their emotional state? Try to put yourself in the scene and imagine what it all looks like and feels like, what other small details exist that can help establish the scene. What kind of ambient sounds are in the area? Are there birds or other animals? Can you hear cars or water? There is so much you can do!

Alternatively, maybe try reading a novel or two and see how the author fills out a chapter. I would also strongly recommend collaborating with people in your roleplay! Open a gdoc and write a post together.