Stuck in Service upgrade

Hi !
I have solved the problem, after having opened an Azure Case and received guidance as well as advice.
The situation briefly was the following:
Problem: there were actually several error messages whose interrelationship unfortunately prevented a straightforward solution:
a. the first one was: (Service Fabric cluster) "upgrade service unreachable", then I detected a second one at "Fabric upgrades":
b. the text was "The current fabric version is no longer supported. Upgrade your cluster as soon as possible. Click to learn about supported versions". My version was 7.0.470.9590.
I mistakenly associated the two and didn't look closer to "Security". In time, I realized that the self signed certificate was expired. This is why the automatic upgrade could not be performed.
Solution: in order to learn from this situation, I chose not to redeploy the cluster+publish the .NET application. Under the supervision of the Azure Support staff, I went through the following steps:

• I checked the cluster VM's (nodes), by provisioning a (rescue)VM in the same VNET and RDP ed in to the nodes to see their health. One of them had not enough free space (logs piled up because of brute force attacks on the node - there was no NSG)
• after having restored the health of all nodes, I performed a rollover of certificates, from the primary (expired), to the secondary (new), as per:
  How%20to%20recover%20from%20an%20Expired%20Cluster%20Certificate.md
  and
  Use%20Azure%20Resource%20Explorer%20to%20add%20the%20Secondary%20Certificate.md
• after having solved the expired certificate problem, I performed the service upgrade to the latest version 7.1.428.9590

Having corrected all errors of the cluster, I published the application on the cluster, with the new certificate.
This ended all issues with the application. The environment was Dev.

I hope this helps others too.