The touchpad still stops working while pressing a key. I fixed it by installing xinput and setting the prop with the command xinput set-prop 13 299 0
I found a solution to this problem, the KDE Plasma Settings Manager Touchpad Input is only compatible with xorg-driver-input-synaptics and not libinput, so installing xorg-driver-input-synaptics allows the function to work.
I don't know if I should resurrect this issue, or create a new one, but I this issue hasn't been fixed. My Synaptics touchpad work fine on Budgie for years. I just did a fresh install of Solus 4.3 Plasma, and some Touchpad options have been greyed out, including tap to click, which I think is mandatory for good experience.
And what was needed to fix it was to install xorg-driver-input-synaptics.
So the same problem and the same solution as in this original issue. Do you think that driver should be included by default, or would that cause a problem?