journalctl has a --output-fields flag that allows for printing of some fields
--output-fields=
A comma separated list of the fields which should be included in the output. This has an effect only for
the output modes which would normally show all fields (verbose, export, json, json-pretty, json-sse and
json-seq), as well as on cat. For the former, the "__CURSOR", "__REALTIME_TIMESTAMP",
"__MONOTONIC_TIMESTAMP", and "_BOOT_ID" fields are always printed.
I wonder if there's a way to ask for "all fields except those starting with _"?