@Baneat
So it turns out that both the iPad Air 5th gen (17.1.1) and the iMac 27" Late 2012 (10.15.7) can disable the EU Voltage limit of the A2155 Apple dongle, and so I got the same volume with both versions (A2049 and A2155), on those two devices.
Whether you may get that 0.5V limit on your Apple device, I can't tell.
All Windows, Linux, and Android devices will encounter the EU limit on EU dongles, afaik.
I highly recommend you get a basic multimeter though, with which you can measure output voltages yourself.
This can be extremely helpful when troubleshooting audio equipment.