One note: Sony is saying the A7R IV has better weather sealing. They've said this with every generation. Their repeat failures here is one of the things that has kept me from giving Sony a shot. If you shoot in anything other than dry weather, I would caution you to wait and see if the A7R IV can actually resist rain and snow. I was torn between the 5Ds and the A7R III right up until the test came out that showed the A7R III leaking like a submarine screen door. For me that killed Sony as a choice regardless of any other technology or consideration. It's ridiculous that Sony can't get this right.
Last time rain hit I was shooting the 5Ds + 16-35 f/4L IS and I didn't even pause or hesitate, I just kept hiking and shooting.
That's such an important point that gets often neglected for many outdoor photographers. Such cameras look nice on paper and in a review, but resistance and durability barely ever get tested or even mentioned. I've dropped my 5d mark iv on rocks and in the mud and it still works perfectly. Those are just things that happen if you spend enough time working with your gear.