Ok folks, after a good breakfast I think to have solved the mystery….
It seems that the V2.J29.S7 FW behaves differently from the V2J24S4 (and 2J25 too) when used with the STM32 ST-LINK Utility.
If there isn’t any target MCU when the “Settings” button is pressed on the STM32 ST-LINK Utility, it appears the previous error (USB communications error).
But if there is a connected target MCU it works as expected.
This is not true with the older FW versions. In this case when a target MCU is not connected the ST-Link dongle is correctly detected.
BTW: I’ve also tested the STM32CubeProgrammer utility with success and then upgraded to V2J30S7 FW using the current STLinkUpgrade utility as stated by Slammer.
Anyway, because I’ve a couple of ST-Link v2 dongle, I’ve left one with the V2J24S4 FW, just in case… 