Quick return to home screen from any screen - Forerunner 245

Yes just hammer the back button 

AFAIK, there is actually no way to go back to the home screen from an activity (apart from pausing/ending the activity). To do that, you would need the hot key feature, which is not present on the 245, but only on the 745/945/Fenix. Typical Garmin software differentiation. 

More like typical software differences from any manufacturer, do you expect Garmin to sell only one type of watch with every feature imaginable? Coros? Suunto? Polar? They sell different models for different needs.  Want lifestyle get a Venu, running get a forerunner, triathlon 745 or 945, multisport then get a Fenix.  Why do people complain when their cheaper watches don't have all the features of the more expensive ones?  

Stop moaning and if you want a device with all the extra features then go and buy it.

Who said I was moaning? It is Garmins business decision to do that, and I can fully understand why they are doing that. I just specifically noted it, because outside of the specialty sports watches world, software differentiation is something done very rarely nowadays (see Apple - every iPhone has the maximum software experience possible on the given hardware). 

There's actually a workaround (that comes at some cost) : disabling the lap button. 

If disabled, pressing the back button during an activity allows to access the home screen ... but you miss the lap button.  

But this is no generic "go back home" shortcut (as requested in the original post), it only helps to step out of an activity view while not stopping it. 

No they don't.  iOS 14.5 has 'limited support on iPhone 6S, iPhone 7, iPhone SE (1st generation)' as well as many iPads so your argument is moot.  Are you saying that Polar don't differentiate between models or Coros because they certainly do.  It just seems that too many people buy a product and then pick it apart when something they want that wasn't even claimed to be on it isn't on it!!  I knew perfectly well there was no hot key feature on the 245 so am not now going to complain about it.

You could put the time data field in

Time should also be a default data page out of the box. Depending on how your data screens are set up, the time of day is your fourth data screen. You can access it by pressing the bottom left button a couple of times.