The problem lies with Darkloader, as stated above, it is outdated and no longer supported by any modern FMs.
Some FMs may still function, but many (most?) modern FMs break using DarkLoader. Sometimes in obvious ways (eg crashes) and sometimes in subtle ways that you don’t even realize.
Switch to AngelLoader or FMsel to avoid these issues.
maybe the problem lies with modern thief 1 missions, since there aren´t many of them
Are you referring to the shortcut near the "little girl" who is in trouble? (trying to speak in spoiler free code here but it's a bit hard).
I actually didn't find MIM to be "hard" - I found the level metrics annoying.
It felt like a nuisance to get around for me. It's constructed as an obstacle course and the congestion later on just makes it annoying in some places.
Like on the positive, the overall tone is excellent and there were a lot of great and novel ideas at work.
I have be...