I hear you, OP. My eldest is 11, and we've had some lovely evenings watching stuff we both enjoy together (His Dark Materials, Harry Potter, Malory Towers even), but also I'm a single parent, with a fairly demanding job (sometimes needs finishing in the evenings), and a younger child who tends to wake around six (sometimes long before), so having to choose between 'time to unwind, alone' or 'getting to bed on time' feels a pretty grim way of living sometimes.
Eldest DC is indeed lovely company, but when I've been 'on' for 14 hours or more, actually I don't want to be actively parenting any more, I want everyone to be in bed so I can have uninterrupted peace.
I don't have a solution (I'm here reading for the answers!), but I wanted to provide a bit of counterbalance to the posters who suggest that losing the recharge time we've relied on for years is no big deal. I guess there are different personal preferences for needing time alone, or for how you want to spend it (even at 11 mine is not reliably old enough for a lot of TV dramas I'd choose for myself).
If it was only DC1 and me, I think we'd start walking in these warm evenings. That's not an option cos DC2 is in bed! But I find him much easier company outside, and I suppose that's something we both enjoy, so that would maybe be me reprogramming the evening a bit, rather than just wishing for what we used to have.
He'd occupy himself with a screen happily enough, but I don't want to do that so close to bedtime (other than v passive TV-watching in the - only - family room). I'm contemplating the suggestion of craft stuff in his room. He's not much of a reader, but I am - might instigate some evenings 'quiet time' in the living room, and I'll read and he's welcome to sit with me reading or making (or, I guess, come September - doing homework!). When time alone has been scarce (eg lockdown) I have found switching from TV to reading is better for me, as you can do 5 mins here or there, plus it fits into my commute now I'm back in the office etc.
The one thing I have done which has helped, is started doing my end-of-day chores earlier, when one or both children are awake. Loading and running the dishwasher, quickly picking bits up off the floor etc - when 'my' evening was a bit longer, I didn't mind doing this stuff while DC1 was in the bath, but now those minutes are so precious (it's the difference between having time for a 1-hr episode of something or not, as you say) so they can come out of the family account, rather than mine.