I don't think this is really a ReShade issue, more related to game files, but I still have to ask.
Half-Life 1 and all its mods run on OpenGL, so they require the opengl32.dll. ReShade uses this (provided that you've set the .dll to read-only) to enable its overlay. Regular HL1 comes with it. Most mods are basically add-ons, so they're just using the base game's files. HL1:MMod, however, is a standalone release which you have to install from Steam.
Here's the problem:
MMod doesn't come with opengl32.dll in the game files on my PC. It still runs on OpenGL without any issues, but it's baffling that the file itself doesn't seem to exist. I've looked up all folders in the game files but the .dll simply isn't there.
One possible case is that the game uses the .dll in Windows' Sys32 files, which might make it impossible for me to enable ReShade with it at all.
Nevertheless, I've tried downloading an opengl32.dll from an external site, hoping that ReShade would be use that, but ReShade recognizes that it doesn't belong to the game and refuses to complete the setup.
Note that I can setup ReShade with the game without the .dll being there, but the overlay doesn't show up when the game is launched. Thought this was a general issue with the mod till I saw other users using it and confirming that the .dll is in fact in their game files. Then I suspected that this was a Win11 issue till I saw a community post on Steam (
steamcommunity.com/sharedfiles/filedetails/?id=2956983226
) which was a guide and the OP was using Win11.
So I'm just utterly confused why I'm the one stuck with this issue. Would appreciate any help.
For reference, I'm using an ASUS Zenbook S13.