On the original question:
sipgate - I've been using them for years for a business number. At the time you could get a local number which is what I got. I have ongoing credit in the account that never expires and no monthly fees. I've got something like £3 left and has been that for several years. I make no outbound calls. Very occasionally I get inbound calls. Not sure if what I've got is available to new customers.
Then there's ONSIM. It's not VoIP but a SIM you can port a landline number to. Given many phones (and mine) have dual SIM slots now, this seems like an option. Just port number, pop in SIM ( or maybe they support eSIM, not sure) and guess you need a monthly or occasional top up to keep it alive. Not used them so don't know if they're any good, what the porting process is like, and whether it works with PN numbers.
https://onsim.uk/landline-sim/
