Is true Decentralization can exist when regulation is must?
yes it is true,they can not.
Regulation is a rule that was set to make a control about something like organization, law, asset and else. while decentralization is a system that have no authority behind it.
it is totally different if we are talking about decentralized cryptocurrency and regulated exchange.
If that is the case, then I can say that in any crypto project, "decentralization ends when regulations starts".