If you are missing an umami note, it's possible you are missing a very common ingredient in bolognese - chicken livers.
These give a meaty, almost sweet flavour.
Soak them in water for a few minutes, then finely chop or pulse in a food processor.
I use minced (ground) pork, beef and chicken livers.
You might also try adding pancetta, to add a smoky tinge.
cooking.stackexchange.com/users/4194/ElendilTheTall
My guess is a good, highly reduced, veal stock; I've found that this is (often) the difference between a really rich, flavourful, sauce and one that is lacking oomph.
cooking.stackexchange.com/users/16833/Dave
In my experience, there is no Bolognese without celery.
I normally use very finely chopped celery stems, and add them after the onions have softened a little.
You can use celery salt too, but fresh celery is best.
There is also something to be said for finely chopped carrots, but the effect on the overall flavor isn't that big.
cooking.stackexchange.com/users/611/Carmi
Not sure what flavor you're looking for, but try adding a parmesan rind.
Pull it out at the end of cooking.
cooking.stackexchange.com/users/5263/Steve
Milk I don't see any dairy listed in the things you tried, but a true Ragù Bolognese (ie, in the style of Bologna, not the British tomato & meat sauce) contains a bit of dairy in it.
It also requires cooking for hours, as you want the meat to completely fall apart.
By that time, the milk's completely incorporated and impossible to distinguish in the final sauce.
cooking.stackexchange.com/users/67/Joe
Dried, reconstituted porcinis?
I've been tweaking Bolognese for a while now, adding those was an AHA moment.
After reconstituting and chopping, I sauteed them with the sofrito.
Very nice.
The chicken livers mentioned above could be the key too, I just can't do it.
I viscerally hate liver.
cooking.stackexchange.com/users/20183/Jolenealaska
A pinch of sugar cuts through the acidity of the tomatoes, also slow cooking improves texture and flavors.
cooking.stackexchange.com/users/21963/george georgeson
Sweet cherry, smoked bacon, heaps of basil and a glass or 2 while cooking helps for a great spaghetti bolognese.
I love adding a chorizo sausage during the slow simmer also!!!
cooking.stackexchange.com/users/33856/Ric
I have dabbled with almost every ingredient I can think of in varying amount to get my Bolognese to taste similar to a restaurant made Bolognese in the italian alps.   Including:PepperSugarSaltTomatos and tomato puree, tinned and chopped tomatosgarliclea & perrins / Worcester sauceOnions & onion gravy granulesdifferent meats, pork, beef and vealHerbs Basil, greek basil, thyme and oreganored wineand most recently balsamic vinegar  These all get close and do make a nice Bolognese. However the secret ingredient is still missing!
secret ingredient in a restaurant bolognese
cooking.stackexchange.com
<meat><sauce><italian-cuisine>
cooking.stackexchange.com/questions/36640
cooking.stackexchange.com/users/20107/Nick Sorbie
Adding chicken livers, pancetta, chorizo or a good highly reduced veal stock can improve the meat, and celery, finely chopped carrots and dried porcinis can improve the vegetable element. A true Ragù Bolognese contains some dairy, such as parmesan rind, and the taste can be improved with basil and wine. Finally, the sauce should be cooked for a long time to allow the flavours to develop. Many ingredients can be added to a Bolognese sauce in the search for an authentic taste. It is considered essential to cook the sauce for a long time.
There are a large number of ingredients that can be added to get an authentic Bolognese sauce. These include celery, veal stock, chicken livers, etc. Cooking the sauce for a long time is essential for an authentic taste.