I have attached a portable monitor to my Ubuntu laptop. The "Portable Monitor, Ultra Slim Portable Monitor for Laptop HDMI USB C, InnoView 15.6” FHD 1080P" works fine at 1920x1080 on my Windows laptop, but is limited to 1024x768 on Ubuntu. I have played around a little with xandr but with no success.
Any suggestions on where to start reading would be welcome.

When COVID calms down a little, I want to be that guy at Starbucks with not just a laptop, but a laptop and a second monitor. :-)

Thanks

Update, I was only missing one step that the instructions I read left out. After the xrandr --addmode, I still had to change the resolution from settings. That wasn't mentioned in 3 instructionals that I found. :-)

P.S.
I really like the second monitor on my laptop.

If this is solved, you should indicate so by editing the subject line. If xrandr --addmode solved it, that's nice, but shouldn't have been necessary. It's an anachronism. The external display should just work at its native/preferred mode.

If you provide the right specifications running as originally, it might be possible to determine what was going wrong and apply a better fix.

I added the solved tag. It is kind of hidden in the advanced edit menu.

Thanks for your help.

I get the struggle with getting your portable monitor to play nice with Ubuntu. It can be a bit finicky sometimes! Have you tried tweaking the display settings directly in Ubuntu after running the xrandr command? It seems like a small step, but it can make a big difference.