Relates to MC-258347.
From their introduction up to 12w17a, when built, snow golems would create a burst of snowflake particles around them. This stopped happening in 12w18a due to MC-10369. While said ticket was said to be fixed in 19w14a, building snow golems still no longer creates these particles (any created are a result of MC-123338 and are obviously not snowflake particles).
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I think snow block particles added in 1.13 are intended to replace snowflake particles.
Can confirm in 21w11a.
Can confirm in 21w13a.
Can confirm in 21w15a.

Affects 1.17

Can confirm in 1.17.1 Release Candidate 1.

Affects 21w39a
Can confirm.