DHH has built his stuff on Linux, which means that everyone using Linux is a fascist.

It looks like this is more like three different messages that are worded a little weirdly, making it have a more confusing single meaning.

The barf emoji (where they used H1, by the way. Why, I have no idea) implies that they dislike either PaperWM or GNOME, likely the latter given that GNOME and KDE Plasma have a kind of holy war thing going on between its users, and this person (who uses Plasma) is the kind of person who has extreme opinions it looks like.

I wish them all the best , except if they're part of fascist open source, in which case, they can get bent.

This part is worded poorly, especially given the preceding barf emoji making you think it's a negative opinion for the whole comment. They are positive about Niri, but IF they turn out to be not very nice then they can "get bent" (whatever that means)

But then again, I have my KDE task manager so that it only shows tasks from the current screen on it, and even I sometimes find that disorientating.

And this bit is just talking about how they won't really take advantage of tiling WMs anyways given that windowed DEs are already "disorienting"

No, I actually have to thank you for mentioning Hyprland bring made by a fascist because that's what I mean by fascist open source. I remembered there being some window manager or similar thing being made by a fascist and was unsure if niri was that or something adjacent.

Hence; I wish it well, unless it's part of fascist open source.

I highlighted the part about paper WM because I dislike how gnomes pseudo space age design ls work, hence the negative reaction.

But I appreciate things existing in the Linux system I don't enjoy because it makes the space more diverse and interesting and a breeding ground for new ideas.

Unless those ideas are fascism.