probably better to ask or browse in the GPS, HRM and Bike Computer
But answer is depends.
My garmin 945 always displays my HR somewhere on the screen when jsut in regular watch mode, and am sure could make it the main dispaly. Also can just press a button and scroll to the HR page.
When actually doing an activity, I can have multiple things, I have have HR as part of he screen, as a whoel screen, or as the only thing you can see at all if wanted.
Maybe go to the DCRainmaker websire and browse a few reviews of watches eg a mid priced watch:
When Garmin first introduced the Vivoactive 3 almost two years ago, I wondered how exactly they’d create a successor to the Forerunner 235. Sure, the FR235 had more buttons than the Vivoactive 3, but ultimately the Vivoactive 3 was a
to see waht it can do