Just got two things to add to this discussion:

One is that I "walked" into a thread that was clearly marked 18+, clearly involved sexual themes, and I pmed the roleplayer anyway. I told them I was interested in the RP but wanted to know if it was okay if we didn't do sex n' stuff. Plot twist: they were okay with it.

Second thing is just my own personal experience. I've tried to start 1x1 RPs at least ten times, and half of them never turn into RPs before my partner ghosts on me. The other half never make it to the second page! I've even tried to do RPs with people who I talk to on a regular basis. Yes [@FamishedPants], I'm talking about you in the Roleplay discussion thread again. Come at me bro! But yea, group roleplays aren't as "intimate" as 1x1 stuff, but they are usually easier to join because the GMs aren't as picky. There's way less 18+ content, no sex stuff, etc. If you're half way decent at writing, aren't an asshole, and are more interesting than a potato, you'll do fine in casual.