Mandatory field added to Teams SharePoint site (lists and libraries) accidently and now can't remove

Please help. In trying to implement a fix for a different problem I have somehow inadvertently added a "mandatory field" which is an integer field and called "User ID" to all Content Types on the site. The site is hosted in a channel in a MS team and I have confirmed that the added field is not in the Parent site (main team channel site). I don't remember how I added it and all avenues I have tried to delete it/make it non-mandatory have failed. I have tried editing/removing it from the Item content type but no options to delete or even save changes for this field are available:

The User ID field below is not selectable:

I have tried the same in the "Classic" experience but still no options.

Further digging shows ALL content on the site "missing" this mandatory User ID field metadata.

e.g. site content pages

I need to find a way to remove this mandatory field from either the "System" (as this is the parent content type for an Item) or the Item content type as this is the ultimate parent for all other content types.

If I can't work it out then I will have to setup a new team channel and copy/replicate/update all the work to date (Power Automate/Power App integration/Power BI Report). Not what I want to do.

Also, while I am a site "owner" I am not a site Admin.

Any suggestion would be appreciated.

Gavin