Up-front, I don’t think this is Monzo’s issue, but it’s an odd one.
When my wife tries to use monzo.me, the credit card fields are read-only so she can’t complete it. The same occurs on any browser on her MacBook Air. However, if I use the same URL on my own Mac, the fields are fine. However, she’s experiencing no other issues on any other sites.
Has anybody seen this or just have any ideas about this?
And disabling any firewall / adblocker type extensions or software (if such a thing exists on iOS)
From the looks of the post I think they have. 
So they did. I was doing that walking a million mile an hour and glancing 
Since iOS 16 theirs a special category for it in the App Store.
This is on a Mac, so not iOS. All the suggestions have been done as well.
If she tries a private browser does she have the same issues? Private browsers typically don’t have any plugins/extensions enabled so it’s an easy way to check if that’s the issue.