The UI is fine once you get used to it. We’ve rented cars a handful of times in last year+, most recently was given a free upgrade to a 2023 Mercedes SUV and the car nav/radio/etc UI was mind boggling and unlike a smartphone. Eventually got used to it, after a day or two. Same when I went down to visit relatives and ride BWR AZ, had a Nissan something and that UI was completely different and also took some adjusting. But once you get used to it, pretty easy to navigate.
last night I played around some more with Garmin and my own custom screens. Just throwing out some ideas and these screen shots are somewhat stream of consciousness until the end:
Stamina screen with real-time power graph and real-time workout comparison:

Think this came with the 840 and I modified it:

This is what I’ve been using on the 530 when a workout is not loaded:

Default workout screen - you need this screen to swipe up and rewind a workout step:

Two right-to-left swipes from default:

This is a right-to-left swipe after the default workout screen, I played around with this one a bit:

variation with gears:

variation with real-time power graph on top row:

just disabled that warning.
swapping gears and power graph (really quick and easy while riding):

840 screen is a little cramped when Varia radar goes off:

real-time HR graph top row, time-to-go bottom left:

swapping HR graph and time-to-go, again this is fast&easy while riding:

By the end of ride, settled on this variant:

Going to try that for awhile.