The HDMI Forum, responsible for the HDMI specification, continues to stonewall open source. Valve’s Steam Machine theoretically supports HDMI 2.1, but the mini-PC is software-limited to HDMI 2.0. As a result, more than 60 frames per second at 4K resolution are only possible with limitations.
What kind of GPU are you using?
Neofetch says that it’s seeing an AMD ATI Radeon HD 8730M and an Intel Haswell-ULT, which is probably the chipset connected to the i7-4600U, and I’m assuming what 99% of the graphics are being generated on.
Try making the move to Wayland. I habe zero issues cinnecting or disconnecting monitors.
If I can do it while keeping Cinnamon, and my current desktop, I might.