Unable to Airdrop photos from the iPhone to my iMac

Over the last week, I've noticed that I can't Airdrop photos from the iPhone [IOS 18.1.1] to my iMac [now running 15.1.1 (24B91)] but I can send files and photos from my iMac to said iPhone. I have tried signing out of iCloud on both devices and making sure Wifi/Bluetooth are on. I can see the iMac in Airdrop on the iPhone but just says 'Waiting' and nothing happens. I have tried with iPad too [iPad to iMac] same problem but fine from iPhone to iPad.

Any ideas what is going on?

[Re-Titled by Moderator]