Random question for GMs: how do you break up the montany?
I don't feel qualified to answer this as I don't remember having this problem, but on reflection, that might be a good thing.
First and formost, you're not limited to combat and skill checks. There's tone, theme, game length, structure (is it mission based, exploration based, dungeon crawl). as well as other things. I've run games from modern horror to high fantasy, Victorian London, James Bond, and soon I'm running a fantasy wild west themed game. My games generally run until level 12 or so, since that's the point where they naturally seem to end, and when I start to tire of the setting. Even within a fantasy setting, you can go grim dark, historic, silly, sci-fi (Barrier Peaks), and many more.
With combat, there's lots of ways to mix it up. It doesn't have to be much. Tight hallways where PCs can't shoot through each other, a guy on a platform or rooftop out of melee range, a wild magic area, or a set of stairs that are difficult terrain unless the PCs leap down them. This kind of advice is generally frowned upon online as it screws over particular players, but I never had a problem with it, and neither did any players as far as I know. The melee fighter would be screwed by window crossbow guy, but in practice it breaks the monotony of running up and swinging their best weapon. I'm also a fan of removing player gear. Disarm, rust monster, mimics, things of that nature. The fighter now has a choice. Does he draw his backup club, or does he make a run for his +1 axe that was just thrown across the room.
This can extend to entire adventures. Escort quests, rescue missions, a race to find some magical item, having to fight enemies with non-lethal means, whatever. Yeah, these are basically the same combat and skill check combo, but they feel different.
Another thing I'm a fan of is utility at a cost magic items. My favourite being an item that grants advantage on a roll, but disadvantage on the next two rolls. Others are weird consumables. Spell scrolls basically, but rethemed to be weird items like statuettes or a necklace. That way the players can choose to use it or sell it. Consumables are great because they don't derail campaigns. They can derail an adventure or trivialise a big encounter, but rarely more than that.