Thanks very much, Dave. In System Settings\ Network\ Connections\ Edit your Network Connections\ Wired, I see that Allow auto-negotiation is not enabled, Speed is set at 100 Mbit/s, and Duplex is set at Half. Well, that is weird. What is the reason for those settings? The Networks item in System Tray says: Connection speed: 1Gitb/s. I tried Network Connections setting Allow auto-negotiation enabled, and I tried speed setting 1000 Mbit/s and full-duplex, but that didn't make any difference. Which is no wonder, as my internet speed is not limited by Kubuntu settings, but by my VDSL, as shown in my router, since a couple of weeks or more. Anyhow, the Network Connections settings in System Settings and the discrepancy with the readings in System Tray are weird.
Sure yvw, I'm sorry the duplex thing didn't help and I hope you can find the cause, If I remember right I only changed the duplex to full but did not change the speed.
I see that those Network Connections settings are default for KDE Plasma, also for Neon. See Wired connection settings , in the Lifewire article How to Configure Networking in KDE Plasma. I don't know why those settings are like that, but it seems default, and I guess it's OK.
I migrated to another internet provider. Not only did this fix my internet speed, but also the weird issue of not being able to connect to Distrowatch. I don't know what was broken in my old connection, but all is well with my new connection. Time to go read a few weeks of missed Distrowatch content.
Another option, if one has a tower or mini-tower (with a spare 5.25 bay) is a Syba mobile-rack that allows use of both a SSD, and a regular hard disk. You can use the SSD for Linux, and the regular hard disk for bare-metal backups.
