Musescore: This is the site I use to find a lot of content for all the instruments. Sometimes it is just right to print and use, but if you want to try editing, download their free software. You can then download music from the site, and change it to your heart’s content.
If you want to see some of the arrangements I have made, follow me here
I use Ultimate Guitar every day. This is great for all instruments, not just guitar. It gives you the chords that the artist is using in a song, so that you know how to play along with them. You should be totally fine with the free version. I have been teaching how to use it during some Zoom classes, but feel free to request a special class on it!
Flowkey is a fun way to play random new songs. The library is slightly limited, but there are a ton of fun songs to try
If you find an app, site, or program you want to share with everyone, let me know so that I can add it here!