Can't set custom resolution using proprietary drivers

I have an RTX 2070 and 3x1080p monitors which have VGA and HDMI connectors. One monitor is plugged directly into the HDMI port of the card while the other 2 are using DP->HDMI converters for the connection.

I can set the frequency of the direct HDMI monitor to 75Hz while I can’t set it on the DP->HDMI ones.

When I was using Windows I was able to set the frequency on all of the monitors (physically the same connection) to 75Hz. Using nouveau drivers I can set the frequency, the only issue is the nvidia proprietary driver which doesn’t want to run like that.

I don’t have an option for 75Hz on the DP->HDMI ones and when I try to force it with xrandr I get an issue:

$ cvt 1920 1080 75
# 1920x1080 74.91 Hz (CVT 2.07M9) hsync: 84.64 kHz; pclk: 220.75 MHz
Modeline "1920x1080_75.00"  220.75  1920 2064 2264 2608  1080 1083 1088 1130 -hsync +vsync

$ xrandr --newmode "1920x1080_75.00"  220.75  1920 2064 2264 2608  1080 1083 1088 1130 -hsync +vsync

$ xrandr --addmode DP-3 1920x1080_75.00
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  18 (RRAddOutputMode)
  Serial number of failed request:  47
  Current serial number in output stream:  48

I also tried to get the edid from my main monitor, read the modeline and add it to the other monitors but I’m getting the same issue. Do I somehow have to load the edid from the HDMI monitor to the display port ones? And if yes, how as I didn’t manage to find a concrete answer. All monitors show as AOC 27BC (all of them ARE the same model).