I think the blue I am feeling is ordinary, to be expected blue - for all the reasons that you outline. I am very very very lucky in that I can work from home, flexibly, the summer is generally my quieter time and my kids are healthy and we have enough money to eat well and pay a small mortgage. I'm grateful for savings, for better communication with my H, for the kids being mature and understanding (most of the time) and for the good weather we've been having which means we've been able to get outside in the garden a lot and for short walks with the dog every day.
I do feel quite lonely, and also in urgent need of solitude. I think I need some proper alone time with no demands made on me first - and I think H does, and we're both suffering from the lack of it. Date nights and time together has totally done out of the window, but I don't feel like he's not interested and it isn't that I'm not interested - we're both just running on empty right now.
When the schools go back I am going to spend an entire day lying in bed with the dog reading and eating cake.