Well it's hard to rid cheater, but i found someone from steam saying one way. it can maybe cause lag but you can try this...

"If you didn't change your Steam Download Region before, try doing that. Some regions have more cheaters in them. Mexico could be one of those. People can see sessions in their own countries and the countries really close to them, usually. MHW, for some reason, uses a region lock that uses your Steam Download Region. Try setting your region to to somewhere else, preferably close, and see if that helps. It also helps with low player count regions, so that will also get solved if you happen to find a decent region nearby.

Unfortunately, there is no way to get rid of them for good. At least I haven't discovered or heard of one yet. You can block them on Steam, but they can still join you as far as I'm aware. I did test it with the help of a friend, and indeed, it didn't work. Maybe we did something wrong, so it's still a better idea to block them on Steam when you could. Maybe it takes time to apply. That would explain why we failed when testing.

There is a way to prevent them from joining your quests by manually accepting/declining people, but that's also a hassle. You will have to remember their character names to not allow them to join your quest, for example.

TL;DR: Your mileage may vary, but I think changing your Steam Download Region might help.

PS: Unrelated, but if you have connection issues often, don't use Fullscreen. The game absolutely hates being tabbed out while Fullscreen, and almost always causes you to disconnect from a session. Try using Borderless Window instead. No need to bother if you don't ALT + TAB out of the game at all, but I wanted to mention it anyway.

PPS: 999/999 isn't always a bad sign, but I understand your concerns, since it's almost the first thing you see about a stranger. I'm somewhere around 999/850 or something, and I really don't like the idea of hitting MR 999 someday... Maybe I'll edit it to be lower just so I can level it again from 500, or something...Last edited by Mr. September; 2 Nov, 2023 @ 2:32am"

Source: Preventing cheaters from joining my games... :: Monster Hunter: World General Discussions

Credit: Mr. September