The sites you mention seem oriented towards discovering what any given plane currently in air is, and who operates it.

What GP is talking about is a site that lists airlines operating that particular plane. A simple, dedicated interface. Drop in an airline, get a probability estimate you'll be flying on a 737 MAX. Or, better, drop an airline, start/stop points and time, get an answer whether you'll be flying 737 MAX.

EDIT: https://airlinelist.com/ has a feature I was thinking about, though not prominently visible. There's a button "No 737 MAX in fleet", which you can use as a filter. So a dedicated website could be just that, with this filter always on.