The long-standing European version of PayPal simply could not be bothered dealing with Brexit in a timely manner and instead relied on a waiver which expired December 2023. FDev are headquarted in and bank in the UK and will have covenants on that banking which prevent them from taking unregulated means of payment.
PayPal are dealing with this -up at their own speed and UK retail customers have now been moved to PayPal UK instead of PayPal Luxembourg, a mere five years after that should have happened.
So as of Jan 1 2024, PayPal ARE now regulated by the Financial Conduct Authority in the UK, so I'd guess the "will return" part is FDev waiting for PayPal to relitigate all their agreements for UK companies and start putting things back together. I expect that will take a while because UK regulation is pretty strong and PayPal are not a bank, so they'll need to get their head around it.