[sciurius]

... so that a fixed size page is generated and that page is rendered as an image which is then scaled to fit the screen. That would be more like how a PDF is handled.

This may be a solution for most, if not all, problems related to chordpro data and differing device sizes. In particular annotation positioning.

So then you would have an identical page on each device, but the text might appear larger or smaller on one of the devices, depending on its resolution and screen density.

This sounds like desired behaviour to me.

This is a less flexible approach and can result in an image on the screen that doesn't match what you might expect, but it might be preferred for situations like this.

I assume that you refer to the screen aspect ratio. When switching between devices that have the same aspect ratio I surely expect to see an identical page.

When devices have different ratios there are two options. One option is to scale to the width, so you get the same visual representation of the song but there may be more or less lines on the screen. Annotation positions will not always match.
The other option is to add an 'aspect ratio' setting and truncate width or height to match.
If this ratio setting would be included in the backup, then restoring a backup on a different device would give identical pages.

When exact page display is not crucial it is trivial to adjust the settings for one song and apply this to the setlist or library.