i have 2 network problems:

- every time i boot or restart my PC, i can't get online. i go into the network settings, and the default route is set to then i turn the ethernet off and on again, and then it works. until the next boot or restart. what's going on here, and what can i do?

- on my macbook pro i have a different problem: sometimes (far too often for my taste) it loses the wifi connection for no apparent reason. it is in the same place, the same distance from the access point, and suddenly, without warning, BAM, no more wifi. this happens frequently enough to be very annoying, especially when watching youtube videos.
different problem, same workaround: turn the network (wifi, in this case) off and on again, and i'm online. why does it do that?

both systems are quad-core i7 running up-to-date ubuntu 20.04,
the PC has 32GB RAM
the macbook pro has 16GB RAM