Describe the solution you'd like
Allow the LetsEncrypt to use local CA provider like the self hosted version of LetsEncrypt - Boulder (https://github.com/letsencrypt/boulder)

and the Project LabCA that uses Boulder - https://lab-ca.net/ Github: https://github.com/hakwerk/labca

Describe alternatives you've considered

to be able to uses the Certificate from Labca or LetsEncrypt - Boulder you need to request the cert with certbot and then add the 90day cert as a custom cert in nginx proxy manger, where NPM is using certbot already to request the cert.

all that would needed to be add is to allow the use of referencing the trusted-root-certificate ACMEDirectoryResourceURI

could also work with issue: Support for Manual DNS-01 Challenge (Custom _acme-challenge TXT Record)