Music Theory Help:
https://www.musicca.com/ (do not need to create an account. Not all features will be available and progress will not be saved)
https://www.8notes.com/theory/ (do not need to create an account. Cannot download sheet music)
https://teoria.com/index.php (do not need to create an account. Progress cannot be saved)
https://tonesavvy.com/music-practice-exercises/ (do not need an account)
https://www.youtube.com/playlist?list=PL9LXrs9vCXK56qtyK4qcqwHrbf0em_81r
https://muted.io/
Ear Training Help:
https://tonesavvy.com/music-practice-exercises/ (do not need an account)
https://www.earbeater.com/online-ear-training/#/ (do not need an account to use standard exercises. Progress will not be saved)
Sight Reading Help:
https://www.sightreadingfactory.com/ (do not need to create an account. Limited exercises available for those without an account)
https://opensheetmusiceducation.org/generate-sight-reading-practice/ (do not need to create an account)