apt autoremove will remove files that are still on your system but are no longer needed because the application that required them is no longer installed, that's why you receive:
The following packages were automatically installed and are no longer required
It is safe and recommended executing sudo apt autoremove.
Generally apt is quite good at knowing which packages are no longer required, but it’s good to see I’m not the only one who reads through the list to see what’s being removed before pulling the trigger 👍🏻
To answer the question, it will probably be better to look through the packages as groups:
The nvidia 435 and 455 packages can be removed if you have ...
Your issue seems to be caused by some obsolete / wrong repositories.
First one (http://ppa.launchpad.net/djart/minidlna/ubuntu) was not updated since 2014, and using it is a really bad idea. You can remove it safely with:
sudo add-apt-repository --remove ppa:djart/minidlna
For the next ones, you'll have to do some source.list editing, because they contain ...
I finally got it fixed.
I had to remove the apt.llvm.org repository from the sources.list. Then I could use the Force Version command in Synaptic to switch over to using LLVM builds from the kisak PPA (which still provides i386 builds of LLVM). That enabled me to reinstall steam, because it could finally get those 32-bit i386 library builds again.