Here are some of the introductory one shots/starter adventures I have run:

Winter’s Daughter - originally for OSE, there is a 5e version available. Very fairy tale oriented, might not be best for hack&slash oriented players.

Village of Hommlet - A classic, can be used as a basis for a long term campaign if you bother with learning the backstory of every villager.

Against The Cult Of The Reptile God - best played as a mystery, with the BBEG revealing itself at the most innoportune moment. Don’t event mention the cult, let the players figure it out themselves. May take 3-4 sessions at least.

A litany In Scratches - Don’t have a lot of prep time? Want to scare the pants of your players? ALIS has almost no combat (at least not until a certain part) and plenty od spookiness.

Broodmother Skyfortress - Out of the box thinking and weirdness galore, this will certainly upend their (and your) expectations.

The YouTube channel Pointy Hat recently had their 100,000 sub special on the Feywild. They created a short adventure (1-2 sessions, obo 3-4 hours each) set in the Feywild. The video it’s attached to is kind of long (~40 min) but is an excellent look at the Feywild. The actual portion covering the adventure gives tips on running it as well. I’ve read it over and it’s pretty well put together.

Video link in case you’re interested. The adventure is in a link in the description.

Same goes for Ginny Di’s Steal This Sidequest. It’s shorter and easier to scale too.

I usually run The Delian Tomb from Matt Colville.

Its got all the classic tropes - meeting in a tavern, travelling through a dangerous forest, crawling ancient tomb turned into a dungeon and fighting goblins. There’s also a lot of great community-supported resources out there for maps and stuff. Here’s a PDF of the adventure

Hey! I run a Dungeons & Dragons club after school at my job (High School Teacher) due to the nature of this club, I have a rotating cast of players and characters, so most of the things we do are one shots! Here are two that I love to run:

1. The Family Axe - basic plot. Starts in a tavern, where the party overhears a group of dwarves discussing how their woodcutting business is going downhill. They’ve lost the family axe, and their brother is missing - apparently the woods themselves attacked their camp, and they haven’t been back. They ask the party to do two things - find the family axe, and bring back their brother if he is still alive. The camp is a few miles away, and is overgrown completely. When the party enters, they are attacked by animated trees and blights. They might find the brother (your choice, I always have them find him, and he says that he took the family axe into the woods to try to stop the woods from being crazy). He points them towards the deep woods, in which the party finds the family axe embedded into the trunk of a Gulthias tree. I always run this final combat with the tree, two swarms of ravens (the leaves of the trees) and a knight (who is animated by the power of the tree, and had been pinned to the trunk with his own sword). This quest is LOOSELY based on a Witcher III quest with some dwarves and a Leshen.

2. Heist: The Appetite’s Hunger - I have a homebrew world in which I run various detective one-shots and criminal one-shots. This particular one starts in a bar called “The Geezer’s Bowels”. The job is to steal a gem known as “The Heart of the Iron Crucible”, which is one of a kind, and from the elemental plane of fire. The Gem is currently on loan to the Central City Museum of [whatever city you want]. There are multiple guards and security systems, so the patron gives the party some passes to case the museum during the day, and they come back at night to steal the gem.

If you’d like maps or resources for either of these, let me know and I can post them!

At the university I run Halloween sessions for new players, and by far the best scenario I’ve run is the first one: House of the Midnight Violet. It’s a 3 hour scenario for a party of 4th level. I’ve run it twice for a party of 3rd level with no adjustments. It’s plays very well as is, though I’d personally suggest running the groups of dolls and cats as swarm creatures rather than individual creatures, for the sake of your own sanity.

One of my favourite introductory one shots was giving everyone an empty character sheet (excluding equipment) and letting them know their characters had amnesia. I’d written up sheets for everyone in advance, and only told them an ability score, or skill score when they actually tried to do it. Might not work for everyone, but it got them to try lots of different things!

In the end everyone had a decent idea of what their characters could do and we took those characters into a more regular game!

Edit: I should add that the actual adventure was rather generic, defend the Abbey against the bandits, with a few simple skill checks for stuff like climbing, investigation, knowledge etc.

I’d make a five room dungeon that basically has 2-3 traps and 2-3 encounters. Since it’s only 2-3 hours you don’t want to have too much set up time of them meeting in a tavern. For a one shot sometimes it’s just fun to say “you’ve been hired to clear the old mine outside of town. The mine used to be used by the villagers as their major source of trade. But the goblins came along and stole it from them.” Then drop them off a little distance from the mine and give them a wilderness encounter before they enter it.

The Adventurer’s League modules on the DM’s Guild that end in -00 are usually good for introducing people to D&D. They usually have a nice balance of role-play and tactical combat, are low level, and are short or broken down into segments. I personally enjoyed DDAL10-00 Ice Road Trackers. It’s four short 1-hour episodes that can be strung together for a larger story arc.