I upgraded from the sony a6400 because I wanted to go full frame, as this system offers a better selection of lenses than APS-C. The camera feels great to use, with excellent ergonomics. The 42mp resolution allows to crop into pictures quite a bit and still be able to have a resolution high enough to print in large format. Only downside is that the camera is a tiny bit heavy compared to the a6400 but that's not a problem for me. Overall, it's a great camera.
The A7RII is a five year old digital camera which image quality are only beaten by five other ones up till the current now, and that is not by much (DXOmark measurement 98 vs the best ones today at 100 points). Canon R5/6 not yet measured by them, might change that position, might not.
The A7RII will be in the history books for how much before its time it was in image quality and it is also the camera that really fueled Sonys progress into being a respected camera maker.
The A7RII is not a do it all camera like the A7III. It is rather specialized for slow paced photography.