How can I track lost/stolen iPhone if its powered off?

My partner lost and his iPhone 12 something or another (this forum lists it as my iPhone XR, IOS 18 which is not the phone in question), we believe his iPhone 12 mini? fell out of his pocket at home getting into his car in our driveway and one of the workers that are spraying for bugs or some other spraying was in front of our property spraying around our house including around our driveway and area where he went on the side of our house where our trash cans are and my partner said he saw him when driving away spraying in front of our house. He didn't realize the phone was missing until he arrived at work and felt his chest pocket and it wasn't there, so without even getting out of his vehicle he drove home and we physically looked to find his phone inside and around the outside of the house.

We couldn't find it so he went to iCloud/find and it told him it couldn't be located and that it must be turned off which in our opinion would only happen if somebody found his iPhone and iPhone wallet and turned it off so it couldn't be traced to it's location with icloud, it gets hazy here because he gets upset easily, but he had an issue logging into his account and is in the process of waiting on some kind of Apple help which tonight he says they won't help him until Feb, 2nd something to do with his account

What should he be doing right now to try to find his phone? I need simple instructions because even though he is 60, he gets so wound up at electronic/digital instructions and goes off on rants when people try to help him, even on me at times and I simply want to help him try to track where his phone has gone off to even though who ever has it has likely turned it off. I've tried calling his iPhone multiple times and it goes straight to voicemail which is one of the reasons we believe whomever has his iPhone has turned it off / powered it off.

Please help, while I'm not the brightest bulb in the pack, I can at least usually follow instructions.

Truthfully now, if the person he suspects has the phone and turned it off, is there anything he can really do to locate the phone online? We do not know the person he suspects has the phone, it is just some guy that was working in our neighborhood as part of a larger company that our leasing agent uses to do grounds keeping and was seen spraying for ants around the outside of our house and along the edges of our driveway at the time we suspect the phone went missing and like they do to all houses in our neighborhoods where we believe the phone fell out of his pocket ... Is there really any chance of locating it if it's been powered down?

Thank you

P.S. It wouldn't normally be a giant problem other than his debit card in his iPhone / wallet (now frozen in his account at his bank an hour after finding it was all lost) along with his drivers license were with the iphone in the iPhone case/wallet, so he is desperate to get it back even if we have to pay a ransom/reward for it to whom ever found it and turned it off.

[Re-Titled by Moderator]