Seems likely, however you would need to run the SSLLABS tester or openssl s_client to say for sure.
The Updater and Backblaze problems are probably from same expired Let’s Encrypt certificate issue:
DST Root CA X3 Expiration (September 2021)
however Backblaze now uses a certificate Valid from Tue, 30 Nov 2021 02:22:14 UTC which might be
causing recent problems. updates.duplicati.com has I think been using Let’s Encrypt certificate awhile.
So when your failure began is an indirect way of knowing which change affected you. A direct check is
A System.Net.WebException: Error: TrustFailure error occurs
and is somewhat experimental, but runs the mono certmgr tool to find out exactly what mono is using.
is what you don’t want, but the exact way of removing it depends on your OS. I have little idea what an ASUSSTOR NAS has inside. Some such systems run Debian, and there’s pretty good info on its use.
If your system is up-to-date, it might already have the required ISRG Root X1, but it’s worth checking.
Extending Android Device Compatibility for Let’s Encrypt Certificates broke mono and older OpenSSL.
OpenSSL Client Compatibility Changes for Let’s Encrypt Certificates
One Debian certificate deletion change that has worked for many people is referenced from this post:
TrustFailure error when using Backblaze B2
Unfortunately the exact procedure is OS-dependent, but the intent is the same. Need to fix certificates.