the mod i have doesn't have a neoforge or fabric, it needs architectury api to load and i need it to be 1.21.1 to be compatible with another mod and there's no forge version for architectury api in that version

Ask the author to port to NeoForge or Fabric instead. The greater modded Minecraft community has moved on to NeoForge, and mods still on OldForge are a rarity at this point.

As an aside, since Architectury API does not support 1.21.1, the author could not have actually made a mod for 1.21.1 that requires it.