I’m trying to use baritone-standalone-forge-1.2.6 with multiple other mods, but I’m not entirely sure which forge installation version I use to run it.

I use latest version of forge and it almost always works(If it doesn't, some mods are uncompetable with each other) for 1.2.x use 1.12.2 forge, 1.3.x use 1.13.2 and 1.4.x use 1.14.4. Hope this helps.

I use latest version of forge and it almost always works(If it doesn't, some mods are uncompetable with each other) for 1.2.x use 1.12.2 forge, 1.3.x use 1.13.2 and 1.4.x use 1.14.4. Hope this helps.

Baritone only supports 1.12.2 Forge, but yes, generally use the latest Forge version unless otherwise stated by a given mod's maintainer. Baritone itself does not have a specific Forge version that should be used because it does not use any of the Forge APIs.