Hi! There is the GUI scale option where you can choose UI scale: 100%, 150%, 200%, etc.

I just installed the game, and it looks impressive. But the lettering is so tiny, for me it's simply unplayable. Is there a way to increase the size of the lettering?

Can't be in standard game as 0ad is pretend-history, but yes in a specific game mode (or mod) it would indeed be very nice.

I haven't read the 14 pages here so my apologies if it has already been mentioned, but I played Scythians recently (don't remember which mod, I guess the Scythian one ? certainly not Delenda Est) and they have no dock ? Is that on purpose ?

I think, @Perzival12 that may be your problem. Maybe reinstall PureOS from latest, try to upgrade, or try another distro, then we can see.