Can't 'return to start' or load course due to insufficient capacity

Morning all,

The last couple of times i have attempted to navigate somewhere, either on the fly (via a 'back to start' request) or via a pre-created course synced from Garmin Connect, my Fenix 5 Plus says "can't navigate due to insufficient capacity". The first time a deleted a load of music and podcasts from Spotify, reset the watch and it worked, but second time, i felt i had already deleted plenty enough last time, and just couldn't be bothered. My questions:

i) has anyone else seen, and been irritated by this?

ii) how much capacity does, say, a 10mi city route (with, i guess, a decent but not ridiculous number of turns) really consume, and what is the capacity of the watch?

iii) is there a way of checking the remaining capacity of the watch, prior to running, to ensure this isn't going to be a problem? (without connecting the watch to a PC and looking at it as an external drive)

thank you vm.