Not everyone needs to be stealthy
I alluded to this in this other answer. Just because you're not the one sneaking into steal something, doesn't mean you're not helping advance the plan.
Think Mission: Impossible
A party only really needs one person to sneak in, steal a thing, and get out. Any more is good for back up but also is another point of failure. Despite what all the memes say, sometimes it's okay to split the party.
So other than the infiltrator(s), what about the rest of the party?
Distractions
There are two guards standing watch over a door. Do you really need every party member to get past them? Of course not! Instead, have one or two party members create a commotion that draws the guards attention away from the door giving everyone else an easy pass.
- Start a fight (or some other commotion)
- Ask annoying questions
- Perform a petty crime nearby
- Put on an impromptu play or display of talent to interest people
And the distraction does not have to be next to the door. It could be across town but needs "all hands on deck" meaning fewer guards to deal with on the mission. Which leads into the next topic...
Removing obstacles
Guards are going to be a major obstacle, but so are normal NPC witnesses, traps, physical barriers, and so on. Anything that a PC can do to remove obstacles can help the overall party's goals. This includes:
- Bribery
- Creating keys for locks
- Casting spells to shape wood, stone, metal
- Animal Handling guard beasts
- Food poisoning the guards so they are either not available or not at their best.
Subterfuge
Spell casters will excel here but anyone can help in this factor.
- Disguise self repeatedly to confuse witnesses
- Silent/Major Image spells to cover areas so people can sneak under cover
- Fog cloud and darkness can also work in some situations
- Kidnapping and dressing up as key personnel to let party members enter restricted areas
- Creating false documents
Research
This should primarily happen before the caper, but since people can't plan for everything, you'll need someone to do quick research to bypass a problem.
- Decipher a sigil that might be a clue
- Have answers to questions if someone is confronted
- Get blueprints to a building
- Learn who has items that are needed (keys, information, tools, passwords, etc)
Coordination / Communication
Now that the party is ready to pull off the heist, one of the most important characters are going to be the person that coordinates everything. No matter how well planned, the dice rolls will fail you at least once. When that happens, you'll need at least one person that can quickly communicate changes and new information to everyone.
That can be spells like message and Rary's telepathic bond, features like race or class based telepathy, communicating through familiars or pets. It could be any combination too.
The sorcerer casts message to tell the Great Old One warlock who uses the Awakened Mind to tell the wizard to communicate with their familiar which gives a signal to the Totem Barbarian that has speak with animals who then walks over to the cleric to tell them to ring the church bell so the fighter can pick a fight with the guards which is the signal for the rogue to sneak in the window.
In the end
Everyone can contribute to the caper. There may not even be any stealth required depending on the plan.