Well, to be honest I tried to make this post work in Catalina:
As just changing "iTunes" to "Music" did not work out I tried to rewrite the script, which was harder than expected 
Now, as I got you the link I also checked on the original post from @Andreas_Hegenberg in this thread and figured out it worked (in my defense, last time I tried it under Mojave it did not ). So my problem is somehow solved by this 
Unfortunately I'm as unfamiliar with this as you are. I kinda was focused on base64 because that's the way I displayed custom icons for now in my widgets.
Anyhow, here is the working code from the other thread:
tell application "System Events"
set num to count (every process whose name is "Music")
end tell
set maxSize to 20
if num > 0 then
tell application "Music" to tell artwork 1 of current track
set srcBytes to raw data
-- figure out the proper file extension
if format is «class PNG » then
set ext to ".png"
else
set ext to ".jpg"
end if
end tell
set fileName to ((((path to application support folder from user domain) as text) & "BetterTouchTool:" as text) & "itunes_cover" & ext)
-- write to file
set outFile to open for access file fileName with write permission
-- truncate the file
set eof outFile to 0
-- write the image bytes to the file
write srcBytes to outFile
close access outFile
tell application "Music"
set playState to (player state as text)
if playState is equal to "playing" then
set trackName to name of current track
set artistName to artist of current track
set albumName to album of current track
if length of trackName is greater than maxSize then
set trackName to text 1 thru (maxSize - 3) of trackName & "..."
end if
if length of artistName is greater than maxSize then
set artistName to text 1 thru (maxSize - 3) of artistName & "..."
end if
set trackInfo to trackName & " | " & artistName
else
set trackInfo to ""
end if
return "{\"text\":\"" & trackInfo & "\",\"icon_path\":\"" & (POSIX path of fileName as text) & "\"}"
end tell
else
set trackInfo to "Music close"
return trackInfo
end if
It gets the title, artist and album too, but that's easy to erase from the code. 