This happened in a multisession one-shot (a game that only consists of one arc/mission/goal that spans multiple sessions) a while ago. It is advertised as a heist mission, thus generally you'll pick rogue and other utility spellcaster that deals with stealth and social interaction. I asked whether there will be combat, and the DM said yes, if you failed your stealth or if the situation calls for it, but all of them can be avoided.
I figured that there will be plenty utility character, but most will not be geared to combat. So, in case rolls gone wrong, I picked a champion fighter, mainly to add durability and as a frontliner. Note that the players picked their own characters without knowing the other characters. They picked all utility spells as wizard and sorcerer, and almost no combat spell or cantrip.
The game involves social interactions to gather information, scouting the treasure room, before finally executing the heist. There are bad rolls, but "fortunately" the heist went rather smoothly. Everyone is happy, but it leaves me slightly disappointed, like I've chosen a wrong character for this mission.
To be clear, I enjoy RP-ing my character during the sessions. However, upon knowing that the other characters are not combat geared, I can't ask my DM (between session) for combat when they roll badly.
I've talked to my DM about this after the game concludes, but he explained that the rest of the party are not suitable for combat, thus he tried to minimize (and actually remove) combat. He doesn't know how to create a combat scene without jeopardizing the rest of the group with TPK. I don't have suggestion either, so I let it slide because the game is already done.
However, I'd like to learn from this situation and prepare when I have such stealth mission with only one combat ready character.
How can I best design a combat encounter with only one combat-ready character, that is a fighter or barbarian (no utility outside combat), without endangering the rest of the group in a stealth mission (like a heist)?