Are Youtube forcing users to use 9:16 Thumbnails in Shorts?

Uploading a short today, and i see this message:

For now, you can’t change the thumbnail on your Short

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a lot of people use wide thumbnails (e.g. 1280x720 in 16:9 format), which can confuse viewers when deciding whether to watch a short or long video.
YouTube I think is now addressing this issue by requiring short videos to have (for now) auto 9:16 thumbnails.

They want us to spend maximum time on their platform and they are pushing shorts to users in every possible way.

krishnaverma said:

They want us to spend maximum time on their platform and they are pushing shorts to users in every possible way.

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Yes, they are focusing on shorts. I received many emails about shorts lately.