Sidebar not showing on LifterLMS lesson – not an issue in other themes

I need help getting a sidebar to show on this page (/ any lessons).

1. This is a brand new, work-in-progress lesson, testing content types etc. – the actual page is set to ‘private’, I’ve cloned it and set it ‘public’ to help with troubleshooting, while I continue work on the actual lesson.
2. I previously used the Cosmos WP theme and had no problem getting sidebars to show on LifterLMS lessons. I haven’t yet tested but I don’t believe this is limited to these lessons. I can test if necessary.
3. The sidebar wouldn’t display so I installed the Custom Sidebar plugin and overrode the default sidebar for LifterLMS lessons but this also didn’t work.
4. I created a new page template with two columns (70/30 split) and as expected, I cannot edit the smaller column in the normal block editor (assuming reserved for the sidebar) – but I can add content directly in the template – obviously, I do not want to create a new page template per lesson.
5. Due to my customised page template, I now have the exact layout / appearance I want for my lessons, but I need the sidebar to display.

Any suggestions? I don’t think the LifterLMS-specific documentation on this is relevant because A) I believe this is a theme-specific issue, which I’m hoping someone can resolve (or ideally, confirm I have missed something very obvious – yes, I have selected the correct sidebar when editing my lessons!) and B) I need to be able to set up multiple sidebars with different content for each lesson so regardless of fault, I need the resolution to be something which allows me to use multiple sidebars with the BlockPress theme.

Any advice on resolving?

Alternatively; anyone else successfully using sidebars with BlockPress? Any tips on what template you’re using / settings you chose?

Thanks all

The page I need help with: [log in to see the link]