I guess I'm braindead but where do I put the files for custom missions? Nothing seems to work...
Into [game's folder]/CustomMissions . Which should contain .json files + a readme only.
DLL goes to Bepinex's plugins folder.
Does this game actually work on SteamDeck? If so, are there any additional dlls I need to install w/ wine prefix?
You don't need any additional DLLs since Proton + whatever it uses for a Wine seems to come with everything necessary for Manaka.
The only thing you should remember is that Bepinex won't work without WINHTTP=n,b parameter.
If you're running Manaka through Steam,
WINEDLLOVERRIDES="winhttp=n,b" %command%
in game's command line options should suffice.
If you're planning to use game mods (and/or uncensored version, which comes with AND NEEDS Bepinex), of course.
(oh, and chainchariot/projects missions repository is accessible for even our country now, thank you!)