I think it's different if you just wanted to use them and not share them with anyone else - that's where the issues come in - but I wouldn't know 100%. It depends on what you want to do with them really

So i can't just have fun with models and should use them only for
content creation in agreement with the developers? (they can give and not give me the right to do some garbage i want to make. If not, i won't get models, right? What if i made them myself?)

I think you should do a mock-up of what you wanted to use the models for and send it to the modmail bot - that would most likely work

For example, today I couldn't do it. Maybe I, of course, tried badly, but it seems that they are not available now. Or is it possible? If so, do I need to ask the developers for permission?

All of these comments can then be removed to avoid clogging up the feed e.t.c.

A bit unrelated to this picture, but I extracted them from the game using UE Viewer - I also got permission from the devs to upload the models to the TTS workshop

Where did you get 3d models from foxhole?