Personally, by "backwards compatibility" I mean, you can continue to use the 2014 Warlock in the same game that your friend uses the 2024 Warlock, and the game will work fine.
This is always 100% what WotC and TSR before it have meant by "backwards compatible." It confuses me a little that people don't understand that. It's exactly what it meant with 4e & Essentials. It's exactly what it meant with 3e and 3.5. It's exactly what it meant with 1e and 2e. It's exactly why the Monster Manual was the same for OD&D, B/X, and AD&D.
All you need to do to take a short rest is spend 1 hour not engaged in strenuous activity.
“We just chill for an hour.” What are they gonna do? Send monsters to attack you? Kill them with your cantrips, then try again.
By this logic, you should never need to rest at all. After all, you'll just handle the monsters with your cantrips, right?
The idea that you should assume an ambush is going to be manageable is metagame thinking of the bad sort. You're making decisions thinking the game is going to act like a game. That's wrong for one because your character doesn't know that to be the case, and wrong for two because the DM doesn't have to do that at all.
After the game. Before the game.
At some point, if you're not happy, you need to say so. The DM is not God or Daddy or the Table King, they're just another person at the table and if they're causing problems, like everyone else, they need a sitting down and a talking to.
At the same time, the DM is also supposed to create a believable dungeon. "We can rest for an hour wherever and whenever," isn't really credible. It's not an MMO where the mobs wait patiently for you to get into aggro range 2-3 at a time. Even if the PCs have rope trick or tiny hut, if you clear 5 rooms of a 12-room goblin stronghold dungeon, why would the remaining 7 rooms of goblins not organize a defense, set up traps, etc.? Why should they continue to obey the encounter-building rules? Or if they're losing, why wouldn't they just take their stuff and leave?
Like either the game is about attrition, in which case resting should have potential costs and risks. Alternatively, the game should not be about attrition, in which case recovery should be automatic between encounters. This whole half-way thing where you need to rest but you can always do it whenever you want doesn't really work.
And if you're trying to say that you can rest but that getting ambushed is an inherent risk... well, that's not really being honest to the complaint that the DM won't let you rest. The danger and additional risk is exactly what they mean by "the DM won't let it happen"!