Works on albums in the Recommended and Library tabs, unfortunately not the homepage (see below)
IMPORTANT
If you don't use the app.plex.tv/desktop URL to access your server, you will need to add your server's URL(s) in the @match section.
To add a URL match, open the tampermonkey dashboard and click the edit on this script
If your URL is http://192.168.1.60:32400/web add
// @match http://192.168.1.60:32400/web/*
If your URL is (https, http)://plex.yourdomain.com add
// @match https://plex.yourdomain.com/web/*
or, for either http/https
// @match *://plex.yourdomain.com/web/*
make sure you add every URL you use to access your server and don't forget the /* at the end so it will run on your music library page.
I'm not great at javascript so hopefully plex uses the same css class names everywhere and this script doesn't break.
Also, plex uses the same elements for all media with the only difference I could find being the aspect ratio (albums are 1:1) so it only works on libraries with only 1:1 posters (music libraries). To fix it would probably mean re-writing it to always check every poster and only swap when the poster is 1:1 and has 2 anchor tags (exclude artist and playlist cards).