Hi!
Is it possible to use the classic packages managment further
in Ubuntu-Mate when I upgrade to UM 20.04 LTS.
Because I removed all Snaps packages, I don't like Snaps so I don't use it and need it.
I use Synaptic Package Maanger to upgrade packages. Want use that further.
I think Canonical is committed to using and ultimately forcing snaps. I prefer AppImage over snaps or flatpacks, YMMV.
The issue will ultimately be that many packages will only be available as snaps and not as debs in the repos. You can always install from source code or move to an "anti-snap" distro like Linux-Mint.
As soon as Linux/Unix starts to gain a little traction, another damn my way or highway war breaks out, as if systemd wasn't bad enough 
I sure hope they can put their ego aside and not force Wayland until it can run on Nvidia drivers.
I had bad initial results with 20.04 on a "gamming" laptop, tried Manjero and it was wonderful out of the box everything worked including the built in microphone which no flavor of Ubuntu seems to be able to figure out (not a show-stopper for me). But the honeymoon was short lived, Manjero uses Wayland and Wayland doesn't work with Nvidia drivers, I need Nvidia drivers for CUDA, game over.
I managed to get 20.04 installed and working quite well after wiping Manjero -- seems there are serious issues with installation on dual video card laptops like this one. By dumb luck leaving the external 4K monitor plugged in during installation I ended up with a usable configuration.
ok 
Ubuntu Mate is rocking 