RTS means real time strategy, it's stuff like warcraft, starcraft, age of empires etc. X-COM is turn based, so not real time.
If you are searching for turn based tactical games (I don't really play RTS), yeah, Mario + Rabbids is very reminiscent of X-COM, only with an emphasis on movement combos (using other characters/enemies to boost your jumps, that kind of things). It does have multiplayer maps, though I have not tried them myself. Main campaign is single player.
In that move combo aspect it looks quite a bit like Chroma Squad, a tactical game with a cast of super sentai/power rangers-like actors who do combo stunts as they move. It's pretty fun, though I have not tried the switch version and I think it's single player only.
Fire emblem has two episodes on switch, three houses and engage. I have played a lot of three houses. It's not for everyone, it's a very long game with loads of dialogue, many characters, a lot of schedule planning etc. Battles are turn based, though in Fire Emblem fashion more about tricking the (basic) AI to break against your high defence "wall" characters while protecting your glass cannons characters. Difficulty being there is a lot of those (admittedly dumb) enemies with various strengths and weaknesses. It's fun but again, single player only. I haven't played Engage, because honestly, Its character design is terrible and it looks quite silly.
Triangle Strategy is another turn based tactical RPG with an heavy emphasis on story. Lots and lots of dialogue, to the point you may ask yourself when the strategy starts when you begin. It has branching story paths, with a rather unique voting mechanic where you have to convince your people to choose the path you want to take. Battle maps are typically less flat than fire emblem, and turn order is determined by each unit's speed instead of being player turn/enemy turn. Again, single player.
Into the Breach is turn based strategy on a very small scale (each battle is 5 turns on a 10x10 map). It's almost more of an open-ended puzzle than a strategy game, requiring you to use your squad effectively to defend key locations against waves of bugs with different abilities. It's very good.
Wargroove is Advance Wars inspired, so instead of unique characters like Fire Emblem etc, you play one commander with a special ability, and armies of nameless soldier units that you recruit in cities you control. A remake of Advance Wars 1 and 2 is on switch too, I have not played it. Not a fan of this type of game personally, but they have their fans. Those are multiplayer, kind of like chess with more rules.
Now for something turn-based and strategic but completely different, Civilization 6 is on the switch, though I don't know how well it works on it. It's Civilization, so long games on random maps where you found your cities, find resources, develop technologies, trade, and choose a way to overpower the other empire. This one is multiplayer.