@MniawY. Thank you for your support and advice. To sum up. Tuneskit said upper limit of use reached, please buy a multi-user licence.
3uTools flagged iOS 14 downloaded as wrong iOS but offered to upgrade from iOS 15.3 upwards.
Woo Techy iMaster offered the options to Upgrade, Downgrade (but only one step down, which is iOS 15.3 as 15.3.1 was loaded), and Backup iOS
What did the trick was iMyFone Lockwiper v3; checked and loaded iOS 14 and finished the job with the iPhone set in DFU mode. I have kept all of the 3 softwares suggested. The request can be closed. Thank you so much.
PS just one correction. Under the Firmware tab, 3uTools offer more backward iOS versions. Not sure if they are Apple-signed.
