hello everyone.
could be an incredibly daft noob question but there is 0 information on the internet. so, in a GUI application (e.g. steam) there is a button to "Open in a folder...", which SHOULD open it in a file manager of choice, right? well, for me it opens in a document viewer - zathura, when i DID NOT choose it. i DO have pcmanfm-qt and yazi as dir openables though! so i checked its xdg MIME association thingie - it indeed says that it is set to open inode/directory FOR NO REASON, and im sitting here and i think im going insane. i tried using the pkgs.selectdefaultapplication (neat app) and it does nothing. absolutely nothing. i also tried adding this line to ~/.config/mimeapps.list file:
[Removed Associations]
inode/directory=org.pwmt.zathura.desktop
to no avail. so, that’s it then, huh? im going to have zathura as a file manager for the rest of my life? oh, well, unless i delete it, of course.
help… please… 
EDIT: in the end… i deleted it
LATE EDIT: since then ive learnt that i can also use:
xdg.mime.defaultApplications
xdg.mime.addedAssociations
xdg.mime.removedAssociations
these little options, instead of editing the ~/.config/mimeapps.list file imperatively.
oh.
uhm. i ALSO had to set a replacement.
[Default Applications]
inode/directory=pcmanfm-qt.desktop
nevermind. fixed! 
nevermind AGAIN. it has gotten WORSE.
on my X session, lxqt, it (the button to view game’s contents) opens in GNOME’s “Open with…” dialogue with “nothing available” to open a folder. i DONT have gnome, and i DONT need it, but xdg-desktop-portal-gtk is SOMEHOW installed on my system?! so yeah now its gone back to level 1 - what am i supposed to do now?
things ive tried:
- GTK_USE_PORTAL = “0” - did f all
- including
pkgs.xdg-desktop-portal-gtk to services.xserver.excludePackages and environment.lxqt.excludePackages that did unsurprisingly absolutely nothing.
ok atm i am looking for a way to delete xdg-desktop-portal-gtk but i cant figure out where it comes from! ok, there is nix-index and rippkgs that can help me find these dependencies (i think???). a few moments later… well, nix-index didnt help. all it said is oh yeah well, xdg-desktop-portal-gtk.service came from… thats right, xdg-desktop-portal-gtk! …ok, maybe sigh its a HARDCODED package/dependancy inside steam? cant be. i checked every single gtk package that i have. im gonna have to “experiment” (my system is incredibly cluttered and i have no idea what i did 5 minutes ago) deleting them ONE BY ONE and checking if any option or package contains xdg-desktop-portal-gtk… ugh. that is REALLY NOT fun. but im sure you guys do even crazier stuff so i gotta try my best…
okay after countless hours and many moonlit ponderings i have finally found the culprit:
xdg.portal.xdgOpenUsePortal
this little guy completely destroyed xdg-open associations… however, this still doesnt explain where does the gtk portal come from…