U3225QE, Magic Keyboard and Magic Trackpad don't work correctly through the KVM function

I've tried to use the KVM functionality of the U3225QE, but it simply won't work properly. I'm using 2 Macbook Pros, and got my Magic Keyboard and Magic Trackpad connected to the monitor.

Just as the manual here (and Dell's support) say, I've connected:

* PC 1 to the Thunderbolt 4 upstream port (#7 on the manual)

* PC 2 to HDMI (#3 on the manual) + USB-C upstream (#8 on the manual)

* My peripherals are connected to the Super speed USB 10 Gbps ports (#9 and #10 on the manual)

I have already checked the cables (using the ones provided by Dell), and both PCs are actually connected and I can make the switch between them (using Dell's DDPM software). The problem is that, on PC2, there's a huge lag in the trackpad's response, and also some of the trackpad's functionality won't work (scrolling with 2 fingers, for example), so I think there's something going on in the transfer between PC2 and the monitor.

Firmware is also up-to-date, and everything is fine with both Macs, so it seems this is something related with this HDMI + USB connection.

In short, the monitor advertises is has a KVM function, but it simply won't work correctly. I'm posting it here since I already went through support, so I'm looking for answers other than "check your cables" and "it's expected the connection via HDMI will be slower". This isn't just some slowness, it really makes PC2 unusable, and at the end I need to manually switch the USB C cable on the Thunderbolt 4 port according to the PC I want to use, which is ridiculous.