Diablo 4 now has a deeper endgame loop than in previous seasons, thanks to changes to progression, itemization, difficulty and the addition of new endgame modes. Diablo 4 is leaning more into the play-as-you-like gameplay style of endgame. The only activity in D4 that is gatekept is the Pit to level the glyphs and to unlock higher torment tiers, however all the other activities are optional.
I have some advice for casual players who are just starting the game or returning players who quit the game long ago but decided to come back. Diablo 4 has a purpose but that purpose is what you want it to be. Every time you log into Diablo 4 you must have a clear objective/goal to reach for that hour, that day, and long term throughout the season. Whatever you are trying to reach as a milestone in D4 to maximize your value of the game should be the reason to log in, whether your objective is to farm mythics, min-max your gear with triple GAs and perfect aspects, chase after cosmetics and achievements, reach paragon 300, try out a new build/class, clear a Pit 150, level all your glyphs to 100, whatever is aspirational for you. Doing brain dead activities all day can burn a player put, but having an objective can make the grind feel rewarding.