As a grumpy old man who wishes his computer would stop changing I've been trying to get on board with XFCE for a while and the big blocker has been making things work well on my 4K screen. (For the record this post is based on Debian testing = trixie, X11, and nvidia proprietary drivers god have mercy on my soul.)
For a while XFCE only supported the type of scaling that makes things smaller. Understandably IMO this confused a few people and happily this has been upgraded and now it also makes things bigger. However in my experience this also makes things blurrier.
In my latest round of testing it appears that the situation can be fixed with a single setting: font DPI.
Settings Manager > Appearance > Fonts (tab) > Custom DPI setting > I chose 150, and logged out and in to have everything take effect.
From this single change everything is looking good in both GTK and Qt apps. I did also increase the size of my panel through the panel settings, and title bars are kind of tiny, but mostly I use maximised applications so I'm not stressing about this too much.
Hope this helps anyone else who is stuck in an "ohgod why couldn't we just stop after Windows 2000" love-hate relationship with computers.