There are a few IPTC editors for iPadOS, but they all need the photos to be placed in the Apple Photos Library, which I do not use.
I use ShutterSnitch, which has 'actions' in which you can make IPTC templates and file renaming templates which can be applied to photos manually or automatically when they are imported into a ShutterSnitch collection. IPTC info cannot be written into raw files, only jpegs but XML sidecar files are created instead.
Then I use iSH, which is an x86 Linux emulator into which I installed exiftools to write the sidecar files into the raw files.
Editing of the photos is done in CapetureOne for iPad. Since the CaptureOne storage on the iPad is a CaptureOne pro session, it can copied to a desktop/laptop for further editing.
Not a simple all in one solution, but it gets the job done.
https://www.shuttersnitch.com https://ish.app
