@imc67 yes, indeed, but the presence of the original DST Root CA is causing issues for Uptime Kuma.
There is discussion in their Issues list, but no solution (some hack proposed but not interested in that).
I've read elsewhere that the old DST Root CA can be deleted ... but no idea how.
That might help Uptime Kuma not to report it.
I might try that on non-Cloudron apps but wouldn't want to try that on a Cloudron app.
Oh well, just some noise in Telegram that I can ignore.