I finally managed to get one of the many tips to work. One issue was that I have ‘Two-Stage Verification’ on my Account Settings. Once I worked out how to get into that, I used this easy tip, and now have access to the Classic Editor every time.
Remember to ‘Save Settings’ though.
If you can’t read that on screen, here’s a link to the original post.
I don’t know how long WP will let that loophole exist, but if you are unhappy with the Block Editor, this will work.