Cannot Add Some Component types due to malformed query

When we try and add custom fields manually we are getting the following error in our logs

`NAMED_CREDENTIAL_REQUEST NamedCallout[Named Credential Id=**********, Named Credential Name=**********, Endpoint=https://**********.sandbox.my.salesforce.com//services/data/v56.0/tooling/query/?q=SELECT+FullName%2C+LastModifiedBy.Name%2C+LastModifiedDate+FROM+CustomField, Method=GET, External Credential Type=EXTERNAL, HTTP Header Authorization=Method: Bearer - Credential: **********, Content-Type=null, Request Size bytes=-1, Retry on 401=True]`

And we are receiving the following back:

`CALLOUT_RESPONSE [44]|System.HttpResponse[Status=Bad Request, StatusCode=400]`

Please see a screenshot of the issue here!