How to export modified video to iCloud?

I am recording video at 4K at 60fps video using the HEVC format on the 15 pro max.

When I upload the video to somewhere like Google Drive, I can choose to upload as 'automatic' or 'unmodified'. The unmodified version isn't great, the colours are pale. On the other hand, the 'automatic' version will modify the file and the colours are much better and file size smaller as well.

Question 1: What is the phone doing when I select 'automatic'? It spends ages 'preparing' the video before uploading it. I thought it would just be converting it to H.265 codec, but if I've already recorded it under HEVC then why does it need to prepare it at all? And why are the colours changing if it's just a straight video codec conversion?

Question 2: Is it possible to upload the modified version to iCloud? It seems to me like I can only upload the original version with the paler colours. The videos are 10-20GB and it keeps cutting out when I try to upload to Google Drive or One Drive. Dropbox works but it's very expensive.