I had a team mate like this literally all day on whats app on his work pc.I've been in that situation, office mate literally writing essays on whatsapp for 40 minutes at a time and scrolling all day - it's a management problem. So many useless, ineffectual managers in the NHS! The only way to deal with it is by moving jobs for your own sanity (luckily I moved to a similar fully remote role, I'll never work in an office again if I can help it!)
We all knew.
Handed in his notice and kept lying when asked how he was finishing everything.
Turns out he hadnt actually done any work for about 4 months, nothing not a thing.
They just believed him when he said he was on top of things.
I on the other hand was drowning in work with zero support and they were on my back every minute of every day.
Another boss mentioned the lack of work done by team mate to my office friend and they quite rightly said well we all knew he was on whats app all day and if bosses hadnt been focused on making my work life hell they might have spotted it.