Question

Does the utility umbrella bypass desolate land/primordal sea?

Answer 1

The Utility Umbrella has never appeared in a game where Primal Reversion exists, so this wouldn't be possible in an actual game. In National Dex formats on Showdown however, it bypasses the effects of regular harsh sunlight, but Water-type moves still cannot be used.

Showdown Replay

In the replay, Cherrim is stuck in its Overcast form despite the extremely harsh sunlight due to its Utility Umbrella. However, it still cannot use Hidden Power Water.

Comments

Exactly, this is also why fire or water moves aren't boosted by the Primordial Weather also.

Answer 2

No, it does not, the item description ignores the effects of normal rain and harsh sunlight, but the primal abilities are not normal "weather" conditions and are treated as "special weather conditions" and is a special battlefield state. So, desolate land is "Special Weather", not "Harsh Sunlight", and Primordial Sea is also "Special Weather" and not "Rain". Since both battlefield states are programmed to be flagged in this way, the Utility Umbrella item doesn't recognize the "Rain" or "harsh Sunlight" flags. This is why fire moves don't get a boost from desolate land, nor water moves get boosted by rain.