I'm currently trying to make an enchanted weapon or find a way to put an enchant ON my weapon. The weapon itself is a homebrewed Greatsword renamed to a Scythe that uses the Greatsword's 2d6 damage dice but also + my strength mod for damage. As of my last campaign I had gotten it enchanted with Cutting Edge which maxes out the damage dice during an attack and has two bonus effects if I roll a Nat 20. Those being it adds another 4d6 rolled damage on top of that plus if my DEX check exceeds the enemy's AC then I can sever one of their limbs as a result of the critical hit.

I'm currently trying to make the enchanted weapon a default item that requires attunement so it functions differently from the base version because of the enchantment on it requiring attunement to work. Ideally it would be best to have a normal weapon with an Attuned property to change the damage from a rolled 2d6+2 to a flat 12+STR or a flat 14 based on whether or not it's been attuned to the user.

How would I go about giving it a default damage value PLUS the strength mod to add to the damage beyond that? I know how to give it base damage, but I don't know how to add the +2 from my strength mod into the item modifier page to make it register that bonus as extra damage. I also can't figure out how to make it have two damage types based on whether it's attuned or not.

Meaning it should ideally have 2 damage effects. 2d6+2 for unattuned and 12+2 for attuned status. If anyone knows how to fix that, please let me know. The sooner the better.

What you're asking for is WAYYYYYY too complicated for the homebrewer so I would recommend not bothering with it and just use custom actions directly on the sheet for damage rolls.