Is there a way to create a custom map marker for a custom structure/biome (same as a vanilla mansion)?

Currently no, MapDecoration$Type is a non-extended enum. You could attempt to make a PR for it, but that would require a lot of work since the value is essentially hardcoded into a specific texture with only bytes to represent some amount of data.

2 hours ago, ChampionAsh5357 said:

Currently no, MapDecoration$Type is a non-extended enum. You could attempt to make a PR for it, but that would require a lot of work since the value is essentially hardcoded into a specific texture with only bytes to represent some amount of data.

Then another question - can I generate a map pointing to a custom structure but with a vanilla icon?

30 minutes ago, FoxBox said:

Then another question - can I generate a map pointing to a custom structure but with a vanilla icon?

Sure, that's how the treasure maps for buried treasure work. Take a look at the shipwreck_map loot table or the TreasureMapForEmeralds villager trade for an example on how to create them.

4 hours ago, ChampionAsh5357 said:

Sure, that's how the treasure maps for buried treasure work. Take a look at the shipwreck_map loot table or the TreasureMapForEmeralds villager trade for an example on how to create them.

Thanks, I figured out how to generate maps