If your Mandalorian test was via streaming, that's also a huge factor. 4K streaming has very poor quality compared to 4K Blu-ray, for instance.
But that’s an unrealistic comparison, because 4K often gets a better bitrate, more advanced codec, etc. If the 4K and 1080P source are both “good”, 4K will look better.
Without HDR the differences are negligible or imperceptible at a standard 10' viewing distance.
I'll take it one step further: a well-mastered 1080p Blu-Ray beats 4K streaming hands down every time.