I've loaded up tons of 1.18 worlds to explore and i have always without a doubt spawned in either a plains biome, a forest biome, a savanna biome, a forest biome, or a jungle biome. If I haven't spawned in those biomes they are near by. I barely see any deserts, dark oak forests,tagia bomes, ect.
This is an opinion, not a bug
(FYI you can only spawn in certain biomes, so checking only that tells you little about the rarity)