External monitor not showing correct resolution - fix it in Ubuntu

I always had problems with my old Benq FP222W monitor. It had it's issues under Windows and I had to tweak around a lot to get the correct driver and the cofiguration right. So I put it away until I recently found it when looking for an extensionfor my notebook screen.
I brought a HDMI cable and - back were the problems with screen resolution. I got a lower resolution which looses quality compared to the native one. This is how to solved this issue on Ubuntu 18.04:

First check the available modes for your displays:
xrandr

I found the right one 1680x1050 missing in that list. Next I asked Linux about the settings it recommended for that resolution:
cvt 1680 1050
# 1680x1050 59.95 Hz (CVT 1.76MA) hsync: 65.29 kHz; pclk: 146.25 MHz
Modeline "1680x1050_60.00"  146.25  1680 1784 1960 2240  1050 1053 1059 1089 -hsync +vsync

To fix this I put in the following commands:
xrandr --newmode "1680x1050_60.00"  146.25  1680 1784 1960 2240  1050 1053 1059 1089 -hsync +vsync
xrandr --addmode HDMI-2   "1680x1050_60.00"

But this does not permanently solve the problem. To enable these settings for a new session I added them to the .xprofile file:
nano ~/.xprofile