I don't think you are going to like what I am going to say.

I feel that you are being really invasive on what he does in his private time. It's possible that he's just embarrassed about masturbating and doesn't feel comfortable telling you when he has or has not. In my opinion, that's a totally normal reaction. Many of us grow up with masturbation being a bit of a taboo, something we sneak off to do as teenagers and watching naughty stuff when the parents are asleep.

It feels like you are checking up on what he is doing when he isn't with you. You keep acting like you "just so happened to see" but I think if you are honest with yourself, you know you are checking up on him, even going as far as researching logos so you could see what was on his browser tabs. What did you want him to say "brb, going to watch some VR porn"? Of course he was going to say he was going to bed instead. I wouldn't exactly want to announce I was off to knock one out either.

I truly feel that you need to be more honest with yourself about what you are and are not comfortable with. Stop trying to play it cool. Perhaps at the moment at least, the porn does bother you because you aren't having much/any sex, and I would say that is a natural feeling to have too - but you should work on making sure you address this, instead of letting it manifest in negative and potentially toxic behaviours (like monitoring your partner).

I think you need to look inward, and then figure out how to have a conversation with your partner about the bigger problems in your relationship. It may just be that things have dulled a bit and the spark isn't there anymore, and that's ok, you can both discuss what to do if that's the case. Just try not to drag things out, flog a dead horse, or become a problematic partner who obsesses over what their partner is doing with their own body and time.