KokoNigel, a lot of that was actually covered (with some back and forth) in this very thread, pages ~7-10.
Here’s a quite damning comparison. The blu-ray literally has a lot more detail than the 4k, lots of detail turned to mush 😦
https://caps-a-holic.com/c.php?d1=5240&d2=15006&s1=48928&s2=156526&x=665&y=172&i=16&a=2&go=1&l=1
And the more famous “detail death by DNR” compare that people were sharing
So, BD has poorer contrast but less DNR and sharpening. 4K on the other hand has better contrast but more DNR and sharpening.