As it currently stands, even if Protection 8 is a possible enchantment, I cannot reach that using only the Infuser. Additionally, despite the fact that Apotheosis allows more than one form of protection on an armor piece, the infuser refuses to allow it. Is there some way for the mod to determine the actual maximum level for an enchantment and automatically apply it to the infuser?

If none of this is possible, maybe a config option could be created in order to manually set the enchantment level the Infuser can enchant up to, allowing modpack creators to simply sync these numbers up with any enchant modifying mods they use.

Alright, so this has been published for both 1.18 (Forge only) and 1.19 now. Since Apotheosis has not yet been updated the feature is currently disabled, when Apotheosis is ready I'll push a new version to enable the support.

Ah, so no fabric 1.18 support? Unfortunate :(

Support for higher enchantment levels will be in 1.19 (and maybe 1.18 on Forge since I've already implemented it in dev there).

Enchantment compatibility carries over just fine. Don't forget Apotheosis allows for protection + one of the specialized versions, it doesn't make all forms of protection compatible. So protection and projectile protection work together, but not fire protection and projectile protection.