OK, so next step tried  has been (thanks Sandro for the input!):

. power down novirt2 where hosted-engine deploy was stuck (and related still local vm), scratching it

. install the same host but with name novirt3.localdomain.local and different ip

. run the

hosted-engine --deploy --restore-from-file=backup.bck

. now all goes ok and novirt3 has been added to engine and novirt1 results as up, while novirt2 nonresponsive (it doesn't exist any more...)

all flow completes

[ INFO  ] changed: [localhost]
[ INFO  ] TASK [ovirt.ovirt.hosted_engine_setup : Undefine local storage-pool 84f8abd5-31ec-4c62-8130-521bb55c41e6]
[ INFO  ] changed: [localhost]
[ INFO  ] Generating answer file '/var/lib/ovirt-hosted-engine-setup/answers/answers-20210827182404.conf'
[ INFO  ] Generating answer file '/etc/ovirt-hosted-engine/answers.conf'
[ INFO  ] Stage: Pre-termination
[ INFO  ] Stage: Termination
[ INFO  ] Hosted Engine successfully deployed
[ INFO  ] Other hosted-engine hosts have to be reinstalled in order to update their storage configuration. From the engine, host by host, please set maintenance mode and then click on reinstall button ensuring you choose DEPLOY in hosted engine tab.
[ INFO  ] Please note that the engine VM ssh keys have changed. Please remove the engine VM entry in ssh known_hosts on your clients.
[root@novirt3 ~]#

Next step will be to try removing one of the two hosts while still all env in 4.3.10 and then take backup of engine and then install the second as 4.4.8 and see if it goes ok.

I'm going to revert the 4.3.10 snapshot consistent env and try...

Problems so far before the next test:

. After the host deploy of the first 4.4 host (novirt3) I see that still the current config results with novirt1 as the SPM and old hosted engine storage as the master domain (I have iSCSI based SHE)

--> all as expected?

. the detach of the old engine storage gives at gui events

OVFs update was ignored - nothing to update for storage domain 'hosted_storage_old_20210827T173854'
Aug 27, 2021, 6:36:03 PM
Storage Domain hosted_storage_old_20210827T173854 (Data Center Default) was deactivated and has moved to 'Preparing for maintenance' until it will no longer be accessed by any Host of the Data Center.
8/27/216:36:11 PM

and the task seems completed, but continues to remain with the lock so I cannot indeed deactivate.... (even after novirt1 put into maintenance to be updated)

It didn't complain that the old hosted engine storage was master and apparently switched another domain (DATA in my case) to master role.... I don't know if related or not

. one not required network was not setup automatically on the new host (in practice in this lab I only have ovirtmgmt and this network...), so when I tried to live migrate VM of next host to be updated (novirt1) I got no hosts available due to that....

I went into setup host networks of novirt3 and added the network and then all went fine: I was able to live migrate and install/add the next hosted engine host (that is the last in my case, no ordinary hosts). Also on the second host I had to go through the setup host networks button.

BTW: I was then able to update cluster and DC from 4.3 to 4.6 and shutdown/boot the VM after that

Gianluca