Ok so I've been with 48 from the start, I know exactly how to switch over to roaming when on holiday, I could nearly do it with my eyes closed.
I was using a "oneplus 6" but recently upgraded to the "oneplus 9 pro"
The problem I have is there's no option to select "when abroad" etc..
Please help as I'm in the UK with no connection
Try these threads:
If they don't help then you'll have to contact 48 support for further assistance.
See the link in my signature below or email them at firstname.lastname@example.org
If your SIM predates January 2023 then you might want to get a replacement in case that helps: