I promised my brother that I'd have a little something to do website monitoring.
Enter: https://metalmonitoring.com
Not only does it monitor the sites, but if something is wrong (especially systematically), it uses AI to tell you what's up in plain English.
Now, I've just started with it, but you can expect that there to be more features, such as monitoring for changes - even on other people's webpages.
There's a free trial period - let me know what you think!
Hope you like where it's headed!