Thanks for the appreciation post and I agree, 4.18 is very good. I started using Linux around 1997/1998 (RedHat 5.0, Dec 1997)…so, I am also old… While I played around with different window managers, I started using WindowMaker very early on and loved the layout and feel of the NextStep interface.
SIDENOTE: I wasn’t even sure if WindowMaker existed still but it apparently just had a new release earlier this month (https://www.windowmaker.org/).
I had switched to Debian in about 2000/2001 after fighting my last bout with RPM hell and in about 2005 I switched to XFCE and setup the side panels in a similar fashion to my WindowMaker layout (sidepanel with widgets, right click menu for everything else). While I have moved my widgets to a top left panel, XFCE has remained my DE for almost 20 years. I keep moving my home folder with each hard drive and desktop change with no real issues. The days are gone when I am interested in resolving issues or trying the next shiny feature. I just want a computer that works when I need to use it. I really appreciate the XFCE team for all their work. I have put in the occasional bug report and the response and engagement from the dev team has been pleasant. I have high hopes that the team continues to value the responsive and clean interface of XFCE while making the needed QoL improvements.
I can only offer some additional troubleshooting steps.
https://wiki.debian.org/NetworkManager#Wired_Networks_are_Unmanaged
NOTE: Unless you know networking, this is probably going to take you down a networking rabbit hole, so glhf.
Some Debian references regarding networking and different configurations:
https://www.debian.org/doc/manuals/debian-reference/ch05.en.html
https://www.debian.org/doc/manuals/debian-handbook/sect.network-config
If you want to stick with NM, it seems you can change the logging level to see if you get more details. I would check the man page or documentation for NM for instructions for debugging. I would expect that you can disable interfaces in NM to reduce the likelihood of some fringe case that is plaguing your setup. Since I don’t run NM, I can’t provide any detailed suggestions.
More of a question but is the switch or router also the same device for the last 2 years? Is it possible that the network device is misbehaving and causing the desktop to lock up? This would feed into @0v0 request to wireshark/tcpdump from a laptop or other device connected to the router/switch to see what’s going on traffic wise.