In the 1.21.70.20 preview, it appears several more cross models have been fixed to be mirrored correctly. However, several of them now have Z-fighting between their old and new models. This includes:
Crimson and warped fungi
Nether sprouts
All potted plants except for mangrove propagules (still mirrored incorrectly), cactus, eyeblossoms, and bamboo
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Can confirm, although they only have z-fighting on some coordinates. For example, if their z-coordinate is at 80 then they will look normal, but place them almost anywhere else and they will start z-fighting.
I cannot reproduce this issue with any of the following blocks from your list when they are not in flower pots:
All flowers
Mushrooms
Saplings
Dead bush
Fern
Nether roots
Azalea and flowering azalea
Here is a corrected list of blocks which have z-fighting issues:
Crimson Fungus
Warped Fungus
Nether Sprouts
All potted plants
Confirmed