The current version of Prometheus in Factory as well as the latest proposed
update to 2.42 (SR#1067528) start the prometheus service successfully. The
/metrics endpoint seems to be working, but trying to open the WebUI
(127.0.0.1:9090/, which redirects to localhost:9090/graph) does only show a
warning:

Error opening React index.html: open static/react/index.html: no such file or
directory

Preliminary discussion is in the discussion to SR#1067528.

Most probably this was introduced by the large update in SR#1057939
https://build.opensuse.org/request/show/1057939

Some things that were discussed already:
- using the latest promu package to build prometheus fails
  (see the errors for openSUSE_Tumbleweed, while openSUSE_Tumbleweed_direct
works)
  - removing the `builtinassets` from the .promu.yml allows successful builds
with the latest promu version, but then the WebAssets are not builtin and thus
missing
- An older bug report for Fedora
(https://bugzilla.redhat.com/show_bug.cgi?id=1902496) mentions the same error

I am currently trying to package the webassets manually outside of OBS, as it
is done on other packages (IIRC grafana).