I use https://concepts.app/en/ for all iPad drawing. It features an infinite canvas, and is tuned for beautiful architectural drawings. I use it for math notes and illustration.

Like my academic colleagues, I was forced onto an iPad (I love chalk and paper) in order to teach remotely. Most of us settled on Notability, too freaked out to learn more than necessary to barely cope. Some realized that one wants all the algorithmic reach one can master, in this new medium. Concepts has many frustrating limitations, but in my opinion it is currently best of field.

In the far future, people will look back on 20th century mathematical notation as a form of sadism (here, look at my crappy machine code, and guess my thoughts!), and they'll mark the pandemic as a turning point where more effective visual forms of explanation first emerged. Playing with Concepts is a glimpse into the future.

While Concepts isn't limited to what can be rendered in SVG or PDF as scalable vector art, one can impose this limit on oneself.

One might have many requirements, choosing an iPad drawing program. My first requirement is that my handwriting doesn't suggest I've suffered a stroke. Believe it or not, this eliminates most of the field. Concepts has a smoothing parameter that makes one's handwriting look better than it would on paper, if one selects 8% to 12%.

I wrote a small SVG filter to convert Concepts artboards to paged PDF documents and diagrams that can be inserted into papers: https://github.com/Syzygies/concepts-artboards

Muse is a bit like this. You can also infinitely nest white boards. It’s really nice, though admittedly I haven’t gotten as much use out of it as I had hoped.

https://museapp.com/

Apple just announced their collaborative whiteboard product: Freeform

It will be available for iOS, iPad OS, and Mac OS later this year. https://www.xda-developers.com/apple-freeform-whiteboard-col...

You can see this app https://renote.so Collaborative work, sharing in web (real time), whiteboards and pages, and other.