The more universal solution would be to standardize Reader Mode compatibility, and for browsers to let users configure how they want Reader Mode to look.

In other words, instead of an n x m solution where every web site has to cater to each different user preference, there should be a simplified content view that every web site only has to support in a singular way, and that allows browsers to cater to the various user preferences.

It's just n x 2 for light and dark themes.

This likely would have happened already if it weren't for Google's hostility to Reader Mode. It's hilarious to see the Reader Mode that they offer, where it's a resizable 2-column view, to ensure that ads are loaded and kept in sight. We get it, Google: you don't want to endanger your ad revenue.