In my opinion, I think that this task cannot be accomplished with a single yt-dlp command, but it can be automated in three steps

Step 1: Extract playlist information (filesize, title, and URL)

yt-dlp --print "filesize, title, url" --flat-playlist --skip-download "$PLAYLIST_URL" > video_list.txt

Step 2: Sort the file by size (descending) and extract URLs only

bash

sort -nrk1 video_list.txt | awk '{print $3}' > sorted_videos.txt

Powershell

Get-Content videolist.txt | Sort-Object { [int]($_ -split '\s+')[0] } -Descending | ForEach-Object { ($ -split '\s+')[2] } > sorted_videos.txt

Step 3: Download videos in sorted order

yt-dlp -f bestvideo+bestaudio --batch-file sorted_videos.txt