Under the EU passporting rules, Holvi as a Finnish Payment Institution is fully authorised to provide services within the EU area. The UK has now left the EU and entered an implementation period. During the implementation period, EU law will continue to apply in the UK and passporting will continue. You can read about this here.
All funds on the payment accounts of Holvi customers are held in segregated client money accounts in European banks. The EU Payment Services Directive has clear regulations on how Holvi must segregate and safeguard its customers' money.
Funds are separated from Holvi's balance sheet so in the unlikely case that Holvi becomes insolvent:
Customers funds will be 100% segregated in client money accounts, meaning that they are not affected at all by a possible insolvency, since Holvi is not the owner of the money.
Customers will be able to transfer their monies at all times.