If you feel that #FDroid downloads are slow, just press ❎ to cancel the download then press Install/Update again so it picks up some other mirror.
There's no unified "F-Droid server" but several and a dozen or more mirrors.
Each time you try again it will use a different one. Hopefully the next one will have better bandwidth.
/PS: We've seen the reports, we will look into it.
I disabled a bunch of mirrors, and the ones that were left were fast. I arbitrarily picked ones close to me, and a couple from other regions I liked the flags of.
Not an educated solution, but it may work until the true issue is revealed.
Go into [Settings] then [Repositories] then expand [Official mirrors] Twiddle sliders to select ones you want to use. By default, they're all turned on. I'm using f-droid Basic
F-Droid
lxskllr
anorax
Tuffi