A fixed model and associated texture are attached which completely 100% fix this issue and all other texture and model based issues with potted cactus (with the exception of it not having outlines like normal cactus). A Programmer Art version of this fix is also attached.
Related issues
discovered while testing
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Hi there!
I can confirm. the cactus bottom texture is smooth while the standard flower pot is rough-looking.

I'll have a fixed version of the model up in a bit.
If you are finished with the fixed model, then please attach it here.

[media]
The attached json and texture file completely 100% fix this issue as well as MC-194950, with no graphical bugs whatsoever. I HIGHLY recommend Mojang just directly apply this fix instead of trying to fix it manually, to avoid any further complications.

Can confirm. (In 20w29a)
Can confirm in 20w46a.

Programmer Art fix attached.
Can confirm in 20w51a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 1.16.5 and 21w08b.
Video attached.

In 21w11a
Can confirm in 21w15a.
Can confirm in 21w16a.
Can confirm in 1.17.
Can confirm in 1.17.1.
Can confirm in 1.18.
Can confirm in 1.18.1.
Can confirm in 1.18.2.

Still in 22w14a.
Can confirm in 1.19.

Can confirm in 1.19 Pre-release 4
Can confirm in 1.19.2.

i can confirm in 1.19.3 and 23w04a