Am I correct that gholdengo with covert cloak should take damage only from hazards, pure base damage, and hail (not taking into account stuff like knock off and skill swap etc to remove it's ability or item)
Gholdengo with covert cloak can only be damaged by these things:
Hail was replaced by snow in scarlet and violet but if it was in the game then gholdengo would be damaged by it.
I don't think Synchronise will be able to burn/poison gholdengo because gholdengo doesn't learn any moves that can inflict those statuses.
Normally soak wouldn't work on gholdengo because it is a status move which Good as Gold makes it immune to.
Hope this helps, let me know if I missed anything.