IRL : I’d argue most security cameras are, AFAIK, on closed circuits. I don’t think they can upload the data somewhere nor keep it for a long time
It does depend. Most big retailers share CCTV footage with each other through a central company to build a profile on shoplifters (though I wouldn't trust them to use it only for that)
Most online shop I know do NOT require a mobile phone number.
This definitely hasn't been my experience though. I can't remember the last time I saw an online retailer that didn't require one, or at least require that the field be filled out. I suppose you could just enter a dummy number but then if there's a problem with the delivery they'll always try to contact you by phone first
They may not give law enforcement direct access but they absolutely upload and share their recordings with third party companies and other retailers. I don't know how long they keep it for but storage space is incredibly cheap these days