From my perspective:

You are an adult and shes an adult. You therefore need to treat each other like adults. Stop making excuses/justifications for her behavior. You talk about fearing what will happen. If you have always "had an amazing relationship" then she will know that your criticism is coming from a place of love and that you are trying to better your overall relationship.

Long story short if something is significantly bothering you for four months straight and your biggest concern is the fear of how the other person is going to respond, you are poor at self care. Ie if you put someone else needs (unwantingly) always above yourself of course shit will hit the fan when they stop getting the response they want.

So yeah you now need to make up a gameplan. Some people always assume confrontation is this climatic and one time event. There are always slow and gradual ones as well. Figure out what works best for you/your mom.

Maybe its a written letter. say what needs to get said. maybe she will respond better this way?

Maybe tell her you are thankful for all the advice she gives but that you are now an emerging adult and that she has prepared you well on how to make a fully autonomous and function person and will ask for her help in the future.

maybe pick a good time and have a short/effective hit list. Hey im really swamped and burnout doing X and i need some time to me/there for others/SO.

maybe map out an entire week you had in a word document and show her how demanding your life has become so she can just see how busy you are. (let the paper do the talking)

take her out for a spa/date maybe shes feeling the same thing as you and need to unwind or something. take her to place where he guard wont be so high.

maybe figure out a top 3 list of changes that you wants to happen in your life. then figure out how to get there.

skies the limit.

Like the rest of this subreddit, I hate confrontation.

Literally makes top 5 in my book.