I would suggest adding the "blocks" label to the report, now that after 1.20.50 it doesn't affect only world-generate blocks.
It seems that custom biomes are alright on their own, but the "multinoise_generation_rules" component doesn't work as intended on custom biomes.
That's why we're able to use locate biome to search for them or the game crashes if you make an error in the JSON (like have "hills_transformation" in the legacy "overworld_generation_rules" be biome that doesn't exist).
They just aren't able to generate because this specific component is bugged.
I believe there is another part to this issue. Normal dirt paths are not getting replaced by grass blocks, as they are on java. 10% of all dirt paths should get replaced by grass blocks if Iām not mistaken.
Java:
[media]Bedrock:
[media]