Here is an interesting music theory site. It seems guitar centric but in reality the chord info is just useful info applicable to any music endeavor.
Note to @ClaudioPorcellana : I’m in ‘semi-lurk’ at the moment, pressing my lurk keys only when I have have anything possibly useful to say …
As a hopeless guitar player, I have used https://www.licklibrary.com/ as a usefull source of instructional videos and other free (if you are a member) videos.
I have 7 ( yes seven !) DVD’s on the modes of the diatonic major scale (imagine sitting through a whole DVD of tutoring on the Locrian Mode …) but there are some open free short videos, done for example by Danny Gill, which although totally for the guitar, can be quite helpful. Here’s one covering the Harmonic Minor and Diminished scales, but focusses on the really useful Phrygian Dominant, which is a Phrygian with a raised 3rd.
Danny Gill - Harmonic Minor And Diminshed Scales - Guitar Tips Session 17 Licklibrary - YouTube
Some of the examples in his various vids are helpful in seeing how these things fit in progressions.