I had already tried switching from categories to list view from the 3 dots but it seems to revert to categories.
Hmm, I'll check if my iPhone does that, it's updating at the moment but here is a good article on the topic;
How to Disable Mail Categories on iPhone
In that article it states; "All you need to do is tap the category that's currently displayed, which is shown in blue, green, purple, or red at the top of your list of mail. This will deselect that category and a new "All Mail" category will appear, which contains all of your emails in a single list." That's a different approach which I was unaware of.
PS. Just checked my iOS Mail app and yes, it had reverted to categories view, even just closing (not quitting) the app returns it to categories. Looks like Apple
really wants us to use this new "option" which, as already stated, I do so not a problem for me but some users will hate it I'm sure