You can adjust the maximum size of the cache so it doesn't grow so big, and the next time you start spotify it will shrink the cache down to the size you specify.
Close spotify, then open for editing the prefs file which is at:
Windows1: %APPDATA%\Roaming\Spotify\prefs
Linux "native"2: $HOME/.config/spotify/prefs
Linux snap: $HOME/snap/spotify/current/.config/spotify/prefs
Linux flatpak: $HOME/.var/app/com.spotify.Client/config/spotify/prefs
Add or modify the line starting with storage.size to the number of megabytes you want the cache to use. For example:
storage.size=512
To limit the cache to 512 MB.
Restart spotify and the new limit will take effect (you'll see the folder shrink down to the specified size if it is already above it).
1 On Windows, the %APPDATA% folder is usually something like C:\Users\<username>\AppData.
2 By native I mean the default package manager that installs things in the default UNIX-y locations, like /usr/bin: things like dpkg (or apt), rpm (or yum), pacman, etc. That is, as opposed to the newer generation of isolated package managers like snap and flatpak which install things into a sandbox.