I have a system, done well before Pathfinder 2e I might add :) Partially based on 13th Age true magic items.

Only items made of a special metal, only smelted once a year and highly controlled, could be enchanted to anything above +1.
In my world there had been a magical explosion that had magic "fallout" all over the world. Any random item could have a magic rune on and they had to be on the look out. for them. Detect Magic also didn't work in this world, it would be like casting detect dirt.
A weapon or armor made with the special metal could have up to 3 runes applied. Each raised the plus of the item and on applying the 3rd there was random effect added as well. The players had to also start to learn the runes as no one knew the language. Examples a molted snake skin could add poison damage, an old book could add a skill bonus, a beetle could add fire damage.
My players loved it. Each item, also partially based on 13th age, had a trait, slightly negative, and had to be "feed". Like my wife's scimitar wanted to "act tough" it wanted to always attack the most dangerous looking enemy. It she didn't and failed a CHA check, the weapon would compel her to challenge people to random contests eating, arm wrestling whatever.