Why is playing some RP is so complicated man?

Alright, I suppose I need to tell what I am seeking first, before asking advises, so there's more clarity. Sorry in advance for sounding dumb, but I am not really a tech savant or anything.

So here's the situation: When it was time of new GPT 4o I accidentally found out that I can try seeing characters of my book (unrelated) acting in situations that weren't in my mind before, so I understand them better. I asked it to play other characters while I try playing one of them, one by one. That's how I discovered some kind of RP, I suppose.

Then, I tried out something different. I gave it full freedom on curating where the story will go, while I will be one of the characters there. I didn't ask it to become a single companion/persona/character. It was playing as for many characters, without me doing much but just to introduce some characters or say that there are some new characters - it was creating them itself. After a while, I got into it, tried out different stories and everything was fun and cool. Until 5 or 5.2 or whatever came out that stupidly refused to work with me and when I told it that it doesn't follow instructions and being dumb (the same way I was telling it to 4o, nothing abusive or whatever) it simply went fully antagonistic. So I switched.

I switched to Claude after looking for substitutions. I found perfect Sonnet 4.5 for myself. It did excellent job at being Narrator, or if you wish, a DM. It was able to create distinguishable characters, be edgy, follow instructions, remember the details and etc. And you all know what happened next.

Since Sonnet 4.5 was gone from the app, I am desperately looking for something that was the same, and I reached the point where I am asking Reddit for an advice, lol.

I was perfectly fine with it's positivity bias, "Claudisms", AI-slop phrases, because I could just edit the message with some instructions to get better output. I am also perfectly fine with paying for subscriptions, even was putting extra credits in Claude just to continue playing, so that's not a problem too.

What I am looking for is a simple chat, where I can enter, explain what I want, start. That's all. I don't understand all this character sheets, lorebooks, other shibbity-shibbity settings in ST. I understood something about API, but models I tried were "meh" after Sonnet 4.5.

I would love to have someone suggesting me full prompts, link to the YouTube guide, or whatever so I can do what I used to do with 4o and Sonnet 4.5. Perhaps, an alternative would be highly appreciated - someone explaining me how to write a proper prompt, step-by-step instructions for toddlers how to use ST.

Anyway, post ended up much longer than I intended, and I kind of feel bad about it. Thanks for reading it, all the best.