There are nearly 1000 open issues and a couple of them are about potential vulnerabilities where the repeated refrain is 'we tried to contact the developer, but there's no response' which makes me... uncomfortable, especially given that NPM was the gatekeeper to a lot of services on my local network.
The cert error is related to outdated python code in the latest shipping version, https://github.com/NginxProxyManager/nginx-proxy-manager/issues/2912 and 2921.
Again, you CAN work around it but the whole radio silence on issues and ongoing issues just makes me uncomfortable with the project and exceedingly reluctant to continue using it because it's unclear what's going on, and why.