I store my Joplin files in e Nextcloud, and a few days ago, when syncing changes, it started to tell me
FetchError: request to https://ecloud.global/remote.php/dav/files/[myemail]/Backups/Joplin/info.json failed, reason: certificate has expired
I don’t know if this is a Joplin error, perhaps, but I do doubt it. Has the certificate, indeed, expired for the cloud site?