Thanks for the assistance, but we're not quite there yet...
I found the Akeba Backup plugin installed on the site, which acts on the entire hosting, even interacting with personal data stored on the cloud installed outside of the Joomla environment...
Anyway, I apologize for the misunderstanding, but I'd like to point out that the Joomla update issue is present on my other site, registered with Joomshaper (Joomla version 5.4.2), on which I followed the same instructions provided here... see hidden text...
Didn't you see that this site was already on version 6???
Can you please safely remove the Akeba plugin and the backup files, since, if backed up to the cloud, it takes up several gigabytes of space? Thanks.
PS: In the meantime, I've disabled the Akeba extension.
If necessary, please resolve the Akeba issue and then close the thread regarding this image issue (for this site), and I'll open a new support request for the other site and the other issue. Thank you.