Referring to Purism Launches Librem 14, Successor to Security-focused Librem 13 Product Line - #39 by amosbatto
the L14 will be able to drive two 4Kp60 displays simultaneously
(one via HDMI 2.0 and one via the DisplayPort alt mode of USB-C)
That may not answer “all” because you may be including the built-in display but the built-in display isn’t 4K UHD anyway (it’s FHD).
PS Welcome to the Purism community.