nelly it is really common for late night exercise to cause insomnia. If you don't get that, you're lucky, but it's not generally recommended, partly for that reason. Yes, most people sleep better after exercise earlier in the day.
Most of the things people have posted are at times I can't do because of me doing at least 75% of the school runs. And most of the suggestions are at that sort of time (or at least, in my area, they are, as I said in my OP).
I've said I'm happy to do cycling, I will try running (but a club is no good for me, partly because of the times), and gym classes, I really want to do yoga, I won't do gym machines but that's just one thing I've tried and leaves me cold. I will do gym classes but there aren't any at times I can get to.
The council gym (nowhere near work or home so I can't get there on days in the office or WFH) does have some classes on my usual day off, I have just checked. I have no idea what any of them are as they are all in code but I can find out, and try and do one when DD starts school!
I've just looked at the web pages for 3 gyms that are vaguely near home: as I said above, one is broken (the website not the gym!), one only has machines, one is the women's running club which though I know it exists, took me several more searches to actually find times for! And when I eventually found it I see that the beginner's time is 5.30... I can see that being a pain for a lot of SAHMs and women who work.
Maybe I just live in a really rubbish area for organised exercise! But I do find in general that group things are pitched at way too high a level for me (except yoga/Pilates and even then I went to one yoga class pre-DCs, having been doing yoga for about 20 years on and off, and was told "oh this isn't a beginner's class, you can't come again" because I wasn't fast enough!!)