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Error 10054 means that the TLS (HTTPS) connection was reset by the remote server. You need to ask your host about it.

However, if your problem only started on Saturday you need to check your TLS (HTTPS) certificate. Is it signed by Sectigo Ltd? If that's the case you will need to either upgrade the software you use to run the remote backup or use a different SSL provider (Let's Encrypt is free of charge and works fine). Here's some background. Some TSL libraries like GnuTLS (all versions) and OpenSSL before 1.1.0 could not understand that even if the topmost root CA (AddTrust) certificate has expired the certificate is still good if another CA in the signature chain (USERtrust) is marked as a root CA itself. This made all Sectigo certificates become untrusted overnight by a large proportion of remote clients which were using these outdated TLS libraries. Unfortunately, Sectigo certificates are among the cheapest paid certificates AND all older versions of PHP and cURL could only be compiled against the problematic TLS libraries. This combination broke a lot of things since Saturday. Both us and the Joomla project were working over the weekend to update our TLS certificates so that our clients don't experience service interruption (some was inevitable on Saturday morning). Again, this really only applies to you if you observed this issue starting Saturday and you have a Sectigo signed TLS certificate.