Knightin'+ is the Steam version. Is there any difference between that version and the web/itch.io version?

Yes knightin'+ is a lot bigger and even the first dungeon which looks aesthetically similar to knightin' is a completely different layout. knightin'+ doesn't allow for oob or wrong warps

trying to finish a run of Knightin'+ to submit to speedrun.com and moderate it