There's a few good options.
Least Complicated: Bear Barbarian. Half damage all attacks except psychic. Decent offense. Good whether you're using feats or ability bonuses. Downside is you have to take hits. Low AC and Reckless attack means you'll get hit often. You can run this class pretty much to twenty and the play-style doesn't change much.
Best Option if you can use all options: Paladin 6/Eldritch Knight Fighter 14. You can pick up both protection style and defensive fighting style. You get heavy plate and shield. This will give you a base AC of 21. Then you can cast Shield of Faith for an AC of 23 for some battles. If you combine this with shield, you can get to a 28 AC at key times quite a few times per day. This is without magic armor. You have access to some helpful spells including a spell that can protect you against energy attacks as well. You'll have access to decent offense with occasional smites. Your saves will be really good with the paladin levels. You'll be fairly well rounded.
Downsides: Con, Str, Cha focus versus Con and Str for the barbarian. Takes a bit longer to come online, though you can get the AC fairly early.
Other than that, it's 5E. You can play almost any tank class, even a ranger, and be effective and have fun. Parties don't need a tank to take on enemies. Battles are fast and furious and it's kill or be killed with little room for avoidance. Either they die quick or you die quick. You can also play a Bladesinger wizard/Paladin for pretty good AC and a lot of spell slots for smiting. A buddy of mine did this and is having fun. He can get his AC when bladesinging and buffed to near 30. This is an Int, Con, Dex class. Light armor, maxed dex, maxed intelligence is an AC of 22 while bladesinging before buffing. With Shield of Faith and shield it gets up to 29 for short periods of time with lots of spells for offenses.
Look around. There are some good tank builds possible. If you don't want to min-max too much, almost any martial class and clerics can be built into strong tank types that are fun to play and effective.