So the early ones A7, A7ii, A7r were all ISO invariant.
From A7Rii onwards Sony started using a dual gain design where by you get a second boost in dynamic range, almost like having "two base ISOs". You'd never know looking at DXO graphs
Sony sensors are invariant after the second dynamic range boost. This ISO point used to be at ISO640 on Sony bodies. In A7RIV it's at ISO 400 and with A1 it seems to be at ISO500.
I shoot at these ISOs because there isn't much point bumping it beyond the second base ISO in camera. Might as well retain the dynamic range and work it in post.
Also forces me make best of shutter speed and aperture. We aren't limited like in film days so I can reduce/drag the shutter speed, burst 4-5 shots and get one fully sharp without much noise.
Anyway that's how I shoot, not that there is a right or wrong way of doing it.