Databases like SQL Server and PostgreSQL (and Oracle) support SQL expression fields right in the table, called computed columns, generated columns, virtual columns, etc.
This idea is to make use of such columns by adding an SQL expression field type, right in the AGOL table/hosted feature layer.
For example, AGOL > hosted feature layer > Data tab > Fields view > a read-only field > properties > SQL expression:
'SEWER-' || asset_num_integer
The other fields would remain editable in ArcGIS apps, which would be ideal.
SQL expressions right in the db table would perform better than other expression mechanisms like arcade or even advanced REST API views.
A related, but different, ArcGIS Pro idea: Virtual Attributes (ad hoc)
