I just typed "what is the dynamic range of the Fuji X T4" and came up with 14 stops.
Colour depth for the Fuji is 10 bit.
And I didn't find anything definitive on the ISO performance in comparison to the Sony. But what I can tell you is that the film simulations on the Fuji are more extensive than the Sony. Modern cameras for ISO performance and colour depth are quite good. If I showed you an identical image taken by the Sony and the other from the Fuji, you wouldn't be able to tell them apart.
On my two Fuji cameras, the X100f and the X T1, I do use film simulations quite a lot. In fact as I think about it, I never not use them. I like Acros for black and white and Provia with some added punch for colour.
You can download "recipes" for colour modifications on your Smart or iPhone, you would be surprised at how many. Fuji is known for this, great colour science out of the camera, and recipes to spice life up.
Here are images from the Fuji X T4, stunning right?
https://www.flickr.com/groups/4518900@N22/pool
Here are images from the Sony A7R lll, stunning right?
https://www.flickr.com/groups/a7riii/pool/
Can you tell the difference in quality based on statistics? No!
I agree that, in general, both cameras the OP is considering are capable of outstanding results. Results that are probably indistinguishable for the average user, at the size they are likely to print.
But at the same time, as a current owner of a high-megapixel full-frame camera (an A7Riv), I do think that there can POTENTIALLY be some real advantages to bumping up the megapixels and/or going full-frame. More noticeable with the 61MP of the A7Riv, but that doesn't mean not there with the A7Riii.
There can also be differences between cameras in features and ergonomics, and the camera with the "better" sensor doesn't necessarily win with regard to those.
The OP hasn't told us about himself, his intended uses of the camera, the focal lengths or apertures he wants, how much cropping potential he wants, the size prints he will make, whether video is important,...
As I see it, here are the wins for the Sony A7Riii:
1) Best lens selection of any system, including many choices from other manufacturers. Sometimes those are cheaper, sometimes they provide capabilities not available in the camera maker's lens lineup (i.e. the new Tamron 35-150 zoom).
2) Best performance if you want to use vintage lenses. Those lenses were almost all designed for full frame, so a full frame camera will best make use of their full potential -- usually bigger pixels, so less stringent resolution needs, and not throwing away 5/9 of the image, as happens if you use them on APS-C. In addition, 42MP gives you more potential for improvement via post-processing (i.e. sharpening without artifacts).
3) Best cropping potential (if you use quality glass, because cropping potential is not just about the number of megapixels).
4) Potential to use pixel-shift, for better resolution and reduction of moire. (Only works well with a good tripod and a still subject).
On the other hand, the Fuji X-T4 has its own advantages, mostly ergonomic and functional:
1) Fully-articulating rear screen, great for unusual angles especially for architecture or macro with the camera used in portrait orientation. Also worthwhile if you wanted to do documentary video (or selfies) with yourself on camera, no assistant, and avoid having to buy and set up an auxilliary screen to monitor yourself.
2) Probably less rolling shutter for video (sometimes seen as the "jello-effect"), because all else being equal (i.e. similar tech, no "stacked sensor" tech on either camera), the sensor readout of the smaller X-T4 sensor is probably faster.
3) X-Trans sensor on Fuji reduces (but doesn't eliminate) moire, so can sometimes be advantageous, especially for video.
4) 240 fps video. Only short clips (a minute or three?) due to sensor overheating at that readout speed, but could be interesting.
5) in-camera raw processing and film simulations.
6) ability to do automatic "focus bracketing" for post-processing "focus stacking" deep depth-of-field, useful for macro or extreme near-far in-focus effects in landscape or architecture. (The Sony cameras can only do that manually or as a tethered kludge, very inconvenient if not in the studio).
If buying new, not in a rush, and your budget can stretch, I'd also consider the full-frame Sony A7iv. Has the articulating rear LCD and some of the video advantages of the X-T4, with the vast lens advantages of the Sony full-frame "ecosystem". (Still no focus bracketing, though (I think).
EDIT: And I think it also lacks pixel-shift).
