Hi Ludo’ ,

I'm not very familiar with newuidmap , but with this service and the 
rootless Podman one from issue #72740 [0] I'm able to:

1. the following rootless Podman hello world

$ podman run -it --rm docker.io/alpine cat /etc/*release*

...

NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.20.2
PRETTY_NAME="Alpine Linux v3.20"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://gitlab.alpinelinux.org/alpine/aports/-/issues"

2. and with guix shell podman compose I'm able to run this Podman 
compose hello world [1]:

$ mkdir data
$ echo hello world > data/index.html
$ podman compose up -d

...

exit code: 0
$ curl localhost:8080
hello world

Please refer to issue #72740 for more details.

I hope this helps in answering your question.

giacomo

[0]: https://issues.guix.gnu.org/72740
[1]: 
https://github.com/fishinthecalculator/rootless-podman-nginx-static-server