I select the content type, filter, select and delete the page using the dropdown menu, then the filter resets and I again have to select the content type in the filter because I am not finished.
The filter should remember the settings until it is reset.
Comments
Yes, that seems like an oversight in the core's Bulk Operations views fields.
A workaround is to use the contrib Views Bulk Operations instead. You'll need to:
That will respect the original terms of the search when you go back after deleting an item.
I would also suggest opening an issue in the core issue queue. You'll need a github account.
By the way, be aware that Backdrop version 1.28.1 has a bug that prevents the opening of the Views fields UI sometimes. You can try and patch your version manually as shown here, or revert to version 1.28.0. There will be a release soon.