To activation tap to click you can add an extra config to xorg-configuration in sddm-service-type part:
(service sddm-service-type
(sddm-configuration
(minimum-uid 1000)
(theme "darkine")
(xorg-configuration
(xorg-configuration
(extra-config `("Section \"InputClass\"\n"
" Identifier \"touchpad\"\n"
" Driver \"libinput\"\n"
" MatchIsTouchpad \"on\"\n"
" Option \"Tapping\" \"on\"\n"
"EndSection\n"
"\n"))))))