@SteveRiggs Here are a couple of courses I encountered on my search for more DSP and C++ for Audio resources:
Kadenze - Advanced Audio Plugin Development with C++ in Juce (by Output)
https://www.kadenze.com/programs/output-teaches-creating-audio-plugins-with-c-and-juce
Not sure about the content quality, but it seems ok for beginners. The Basic Course is free btw...
Hack Audio - Creating Audio Plugins with JUCE
https://www.hackaudio.com/juce-tutorial/juce-info/?wlfrom=%2Fjuce-tutorial%2F
Purchased it, but it's very basic tbh.
However the Hack Audio DSP book is quite interesting:
Hack Audio: An Introduction to Computer Programming and Digital Signal Processing in MATLAB
https://www.amazon.com/Hack-Audio-Engineering-Society-Presents/dp/113849755X
The DSP courses on Coursera are good as well. they are mostly free, so it doesn't hurt to take a look at them.