Upstream bug report: https://github.com/grafana/agent/issues/2641 (This isn't fixed in the latest version because the PKGBUILD doesn't use upstream build flow)
package version(s): v0.30.1 (it probably started with v0.30.0)

Description:
When grafana-agent is run with a config which involves scraping systemd's journal the following warning is displayed:
"grafana-agent[548]: ts=2022-12-23T16:04:10.579500851Z caller=journaltargetmanager.go:29 level=warn component=logs logs_config=default msg="WARNING!!! Journal target was configured but support for reading the systemd journal is not compiled into this build of promtail!"
As a result journal entries aren't being read anymore.

It seems that a 'recent' change to promtail build behavior is causing this, I briefly looked at promtail PKGBUILD and it doesn't look like the change was accounted there as well, which means that the promtail package has probably (**I didn't test**) broken systemd scraping too.