The issue is definitely the expiration of the old CA. However, the web browser seems to pull the correct certificate from the firewall (nextcloud is behind HAproxy). It is from ISRG Root X1 → R3 → my wildcard cert. However, the application seems to want to access some local copy of the certificate…

For others (like me) who take too late to actually read the bugreport, the solution is to simply browse to your Nextcloud URL in Edge Browser. After that I was able to login using the Nextcloud client successfully.

Letsencrypt ISRG Root X1 local lookup not found

📱 Desktop & mobile clients 💻 Desktop

devnull October 1, 2021, 9:15am 10

Perhaps solution for linux clients and linux servers (similar problems):

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