I have the same dog! I found this boxer running down the road brought him home his was exhausted from his adventure seemed like a perfect angel! Ha! We found the owner he lived in an apartment asked if we wanted to keep him which I didn’t because I promised my husband no more dogs so we could travel. But I gave in he goes from morning until night unless I wear him out at the dog park or take him for a bike ride…we also go on multiple walks during the day ( I’m also retired) but he will whine and whine to get his way until I firmly tell him no…I also brought in a trainer who uses an e-collar I use only the vibration to get his attention when we are out or the lowest setting and I test it on my own hand first that has helped. He will calm himself with a firm no and then lay down but only after a good walk or bike ride…my trainer always says they can’t go have a beer or go to the gym to get the energy out so I guess that’s true. Also I switched him to homemade food and added potato which seemed to help also.She definitely sounds like a handful! We had one boxer in the early 2000's who couldn't be crate trained and it was a huge challenge so I can relate. (Being 20 years younger sure helped LOL)
It sounds like you have lots of experience to draw upon, which is great! When we got our girl Lena, the breeder told us that she was going to need a firm alpha energy from us. She was right, of course, and it's paying off. It sounds like your girl needs the same thing.
Daycare sounds like a good idea to give you a break, but based on your descriptions it sounds like there is still an issue that more exercise and stimulation won't fix. If she is doing things like counter surfing and being destructive then she needs clearer boundaries.
If your girl can't be confined it sounds like unfortunately that will require more hands-on training. Strong commands like "place", "stay", and "wait" would be priorities for me. I would want to teach her to basically calm down when I tell her to. I would also try rotating out toys so she only has a few at any one time to reduce overstimulation, plus it keeps them fresh when they come back into rotation.
We were giving my currently 17 month old boxer Lena more freedom from her crate a few months ago, but after she started suddenly ripping the bottom dust-cover fabric off of our dining chairs we took a few steps back. She's in her crate more now and we're all happier including Lena. No more destructive issues for 2 months now. She had too much freedom too early and couldn't handle it.