Package manager error "but no such entry exists in the manifest"

Tooling Package Management
6

Nope, that not Revise (no surprise)

(jl_50415E) pkg> add Revise@3.5.2
   Installed Revise ─ v3.5.2
(jl_50415E) pkg> add SpecialFunctions
  [276daf66] + SpecialFunctions v2.3.1
#  works fine here too

By the way, we have the same standard LOAD_PATH:

julia> LOAD_PATH
3-element Vector{String}:
 "@"
 "@v#.#"
 "@stdlib"

So it looks like something became corrupt on your system.
You might want to try to remove and add the registry again
(from Pkg cannot find registered packages - #2 by fredrikekre)

# Remove
rm(joinpath(DEPOT_PATH[1], "registries", "General"); force=true, recursive=true)
# Add
import Pkg
Pkg.Registry.add("General")

But that probably won’t be sufficient.
Otherwise, you can try this ?