Notability supports two screen formats that maximize the visible screen area during screen sharing: Screen share mode and presentation mode. These are available only when you share the screen of your iPad Pro with other devices or via a video conference.
The "screen" format works on an iPad Pro in "Screen sharing" mode. It has a paper size of 24cm x 17cm, which is close to but not quite 4:3.
The "presentation" format has a paper size of 24cm x 13.5cm, which is a standard 16:9 format. So instead of this, one could simply use most modern 16:9 slide templates (such as PDF presentations exported from popular presentation software such as Keynote).
For each format, there are three templates for creating slides in the Notability App. All three template variants come in a one-page and a multi-page template (that is, 50 pages).
You can import the templates into Notability and then use them to create ad-hoc lecture or presentation slides. When using the multi-page templates, simply only export the page range you have actually used (and this assumes your presentation has at most 50 slides).