When I lost my sense of smell, it was kind of just gradual. My main symptoms (basic head/chest cold type) lasted about 4 days, then started to clear up quickly. A few days later I started noticing that I couldn’t smell anything at all.
Not even the most pungent stuff - garlic, peanut butter, fish sauce, nothing. Strangely, though, I generally retained my ability to taste. Certainly it was muted in the same way it’s muted when you have bad nasal congestion, but I could still tell salt/sweet/acid/alkaline.
After about a month my sense of smell started gradually returning, and finally I was able to tell various herbs apart (daughters blind tested me).
I thought it was fully recovered, but it’s hard to know for certain. What I mean is, I don’t know how to prove to myself that it’s “just as good” as it used to be.
This was from an earlier (May 2022) bout of Covid, by the way. I got it again in September 2023 and had a similar course (again just basic head/chest cold symptoms for a few days) but no new impact on my sense of smell, thank goodness.
My wife had it with me both times and never had smell impacted, but the May 2022 episode did kill her sense of taste for about 2-3 weeks following recovery.