Convert h.265 to h.264 how will the video quality change?

Question

H.264

Source video from iPhone:
.mov
HEVC h.265
4K
60 frames
variable bitrate around 85000

I will convert using Adobe Premiere Pro 2020 to
.mp4
4K
h.264
4K
60 frames
variable bitrate around 85000

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Actually, almost all parameters remain the same, except for .mov on .mp4 and h.265 on h.264
Question. How much will the picture quality change?

Answer 1

Depends on the content. Any recoding is a loss of data, so the quality will change for the worse. Depending on the encoder and preset, it may either not change visually, or it may deteriorate greatly, up to squares on the frames. Try it for a short time and see for yourself

Answer 2

Doesn't the h265 codec offer better compression (lower bitrate) than h264? From 30-50%?
From personal experience in video surveillance installations - h265 2mb / s - approximately equal to 3-4mb / s h264 (depending on how dynamically the scene changes)