I’d go for Newgale and White Sands in Pembrokeshire
Never that crowded, really beautiful. Loads to do in the area but no arcades or in your face tourism. I like St Davids good for a coffee or meal. Rib trips area popular activity. Depending on when your going the Islands are great for birds like Puffins and Gannets even if you don’t normally go in for birds
Only 2 possible catches
no real mountain biking near by, but I assume thats not an issue at the moment.
Newgale in particular is quite tidal, with the high tide line covering all the sand
Cornwall has loads of great beaches but in general the summer crowds put them behind Pembroke unless you want more reliable surf
in Cornwall I’d go for Gwithian as that never seems that crowded
Have to say I’m less good on Scottish beaches
But I’m putting Pembrokeshire above the LLyn, North Wales, mid wales, Devon, North Yorkshire and Northumberland
Runs for the exit