I have been experiencing this for a while on my Phone Pro Max 11. When I airdrop from my phone to Apple TV or Mac Pro late 2013 desktop, or to iPad Air 3 latest generation, the video clips become 10 times slower. I.e., a 41 seconds video becomes 4.1 min long, not only on the device to which it has been transferred, but ALSO on iPhone (the original video has become slow motion). It is like the act of transferring activates some type of slow motion feature.
So I checked the video: on iPhone I opened a video that I had already transferred with the results described, then clicked Edit (top right). Below the video clip there was a series of vertical bars, the central ones being more far apart than the ones at the sides. This indicates that portion is in slow motion, basically almost the entire clip. The bars will show only if the video is in slow motion. You can adjust to regular speed by moving the bars together and save the video. However, when I resend the video after this adjustment, all happens again! The video will convert back to slow motion in iPhone and transferred copy is in slow motion.
So, I found it is better to correct in Quicktime by opening the clip in the download folder (where it is transferred when airdropping to my MAC), pulling together the bars (Quicktime will show them as well during playtime) to eliminate the slow motion, than saving the clip in a folder/location of choice. All worked nice until in the destination folder above the saved video clips an image icon with the same name of the clip appeared, with extension AAE (i.e. IMG_0786.MOV and IMG_0786.AAE).
When I opened the AAE file my iPhone library pops up for a sec, then a white screen with written on top "Import", and just below "Import to: Library" with Library being in a scroll down.
Well, once I opened that AAE file, the trick of eliminating the slow motion in QT and saving under a different name (or same name to different folder) no longer worked. The saved file is still 10 times longer.
I have been in talks with Apple support and they will reach out. They suspect something related to Quicktime player.
Apologies if my description is confusing.