I installed DW 2020 and it seems to be working for me so far. Nobody has reported an issue for that update yet, but it just came out.
It did include an option to keep CC2019 installed when I did it, so you can always run both.
I think the update on the server message probably has to do with the default "live view" that they use. I think if you change it to design view it won't give you that message. I prefer design view anyway.
It could also be your site settings in the advanced tab if you have it set to automatically update files on the server when saving.
Either way it is probably fine to click "OK" to that message if you don't mind the extra time it takes to upload the files. I just turn off those two settings to prevent it and put files manually when I'm ready.