I can confirm that the server can generate the world type, it just can't generate one from scratch like @Saiirod said. Upon further digging, it looks like the server doesn't set the world generator type correctly if it makes one itself. It sets it to minecraft:overworld, even though level-type is set to AMPLIFIED. However, the singleplayer generator sets the world type to AMPLIFIED correctly, and the server can properly generate more of the world.
So world generation works in pre5, opposed to 20w21a where it didn't work at all.
I can attest that @Saiirod is correct. Amplified and largeBiomes don't generate on pre-release 2. HOWEVER, I can generate both world types on a 20w20b server. That was the last snapshot in which it worked.
I can confirm that the server can generate the world type, it just can't generate one from scratch like @Saiirod said. Upon further digging, it looks like the server doesn't set the world generator type correctly if it makes one itself. It sets it to minecraft:overworld, even though level-type is set to AMPLIFIED. However, the singleplayer generator sets the world type to AMPLIFIED correctly, and the server can properly generate more of the world.
So world generation works in pre5, opposed to 20w21a where it didn't work at all.
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