I don’t know if these are well known, if they aren’t, give them a try.
Tomato sauces, if they are a bit bland try adding a dash of soy sauce.
If you want a ‘Beefier’ taste in a dish, add Vegemite/Marmite, it’s all umami and really helps. You can make Vegetarian French Onion Soup using it and meat eaters will love it.
Mushroom soup/ sauces, add cinnamon (preferably cassia, not true cinnamon). Just a small amount, below the threshold of where you can identify it as an ingredient. Iirc something about the phenols in the cassia boosts the mushroom flavors.
ETA: based on another comment, chocolate sauces/ Ganache, add vanilla and espresso. If you want the most delicious Reese’s peanut butter cup cheesecake, ice cream etc. You want a shot of espresso and a touch of vanilla.
If you have not tested yourself to see if you are a Supertaster, you should. It makes a world of difference when you are cooking for other people.
If you have others please add them, these are some of my favorites.
Don’t write off vinegar just yet, but try apple cider vinegar or my favorite removediang or other aged rice wine vinegar. removediang is definitely a secret weapon in my kitchen arsenal that I use even when not shooting for Asian inspired flavors.