This appears to be some confusion around this > "All other methods, simple one line filter in the functions.php file or a third party plugin will not work."

Even on this post there are conflicting views. I'd like to be more certain before I advise the 40 sites that I currently manage but for now I am erring on the side of caution and using the classic editor.

Some theme and plugin developers are more proactive which is great but this looks to me the biggest single important change to WordPress in more than 10 years.

I like the longer term direction but having to manage the transition in the shorter term will be interesting. Some of the other 150 or so sites that I've worked on might need some help and it is those people I'm thinking about.