Good notes has an option to revert to v5 and I haven’t had any issues so far staying on v5.
I thought they also had a one time purchase option for v6 but it’s been awhile since I looked.
They did the switch better then notability tried to do. Notability tried to switch otp users to their new plane after a grace period of a year. They caved to backlash and added a legacy plan for older purchasers.
Don’t know if it works for this but have you tried jdownloader 2? That’s what I use for most things. It can scrape pages and maintains a download queue
To semi automate downloading all the pages, try jdownloader 2. You probably need to paste the url into jdownloader manually for jdownloader to load all the downloadable bits it finds on the page.