Thank you, thank you, everyone! You've made some great suggestions, and also pointed out a number of issues.
If I decide to go back to W7 for my daily driver it would mean reverting to old versions of my apps, and that is likely to lead to compatibility issues with all the stuff I've produced since W7. That's a bit of a show-stopper for my Delphi work: I wouldn't be able to build any of my more recent apps, which rely on the latest versions of various 3rd party components. Also, I like using VisualMicro for developing Arduino stuff, and again, I'd have to give that one up.
I think I could dig up a suitable office suite, graphics editor and audio editor. Probably a video editor as well. However, they would all require that I eschew the various advancements and improvements that I've come to take for granted. Thank you to those who suggested what email and Web clients to use, plus the advice about security software - much appreciated.
So it boils down to this: I very much like modern-day Windows apps; I think the range, the choice, and the quality are generally excellent. But I don't like modern day Windows. The conundrum is that if I go backwards in time with the OS, then for compatibility reasons I'll mostly have to go back in time with my apps, as well. In general I cannot expect to use the latest applications on a 15-year-old operating system.
I've made a decision: because of the issues that have been raised, I am not going to dump W11 and install W7 on my daily driver. Instead I'm going to build W7 in a virtual machine, and then in slow time see if I can put together a suitable set of applications.
As a result I'm going to mark this thread as "Resolved", although of course it won't be closed to further posts if anyone has something they wish to add.
I also want to say a big "thank you" again to everyone who has contributed.