They recently changed it to having to wear a mask also on the beach, even when sunbathing or paddling in the sea. You can take it off when swimming only. The report said this is the new normal for Spain and the Canaries for the foreseeable future. That was last week so not sure if it's changed since then
I love Tenerife and go twice a year. Last summer was good in spite of being quiet, I only had to wear the mask in shops, transport, going to the bar or toilet inside. I was in some bars where no mask was required and it was very relaxed, live music and I could stand at the bar. Just before I left they made wearing masks outdoors compulsory, but you could take them off when on the beach or sunbathing around a pool. Since then they have tightened the rules as stated above.
I was due to go out in December but after having an antigen test they changed the rules saying it wasn't acceptable so I had to cancel. I had friends out there and there was a 10pm -6am curfew and they could only sit on the terrace of bars and at 50% capacity in groups of four. They made the best of it but I'm glad I didn't go.
The mask ruling outdoors is ridiculous, sunshine and vitamin D is beneficial and if it remains in place it will kill the tourist industry dead.
At the moment UK citizens aren't allowed in unless they have a residency and have passed a test. There are extra restrictions in place until April 9th, after that who knows? Anybody thinking of going if things ease enough have to be aware that the vast majority of bars and restaurants, shops etcetera are closed in the tourist areas and won't open until the hotels open and start to fill up. This was the case last year.
This website is quite good for up to date information.
https://www.janetanscombe.com/restrictions-in-a-nutshell