Hi everyone,
I've also came across with the same issue with my 4K monitor during installation and instead of connecting to an external monitor for installation I found another way that may work for you too.
I have a dell precision 5510 with 4k display.
When you download the ISO file, Open it using an ISO editor like anyburn for windows or unixmen for linux , after that navigate into /boot/grup/grup.cfg on the line 22
change the ' set gfxmode=auto ' into set gfxmode=800×600 or 1366×768.
save the file and make a bootable USB from it.
when you try the installation again it will force the boot into the resolution you set not on what it detects!
Hoping this will fix the issue for you guys like it did for me