Chosen resolution does not permanently set. Mint 20 xfce.

After a successful mint 20 xfce install, I chose one of the display resolution options..1366x768.. but after not using the os for an hour and then turning the monitor back on, the display shows another choice, 1200 by something. If I set the resolution to 1366x768 and then restart the pc, resolution stays at 1366x768. I have disabled all sleep modes with no success. I can go the xrandr route, but since the display feature shows 1366x768 as a default choice, I'd like to go that route if possible.
Please give me some ideas, thank you.