Can't connect Sony Handycam DCR-HC40 to late2015 iMac

Since it last worked , what has changed ( if anything)?

Have you updated/upgraded your OS ?

Have you updated your version of iMovie.

What OS are you running now and what version of iMovie.

The more info you give the better the chances of a fix.

Just saying, that if nothing has changed since it last worked then it is still supported.Could you by chance be running Monterey 12.3 or 12.3.1? If so update to the latest version of Monterey.

Any chance that the FireWire to Thunderbolt cable has failed?

There was a bug in 12.3 and 12.3.1that prevented tape capture, but your 12.5.1 includes the fix for this.

Other posters on here have confirmed that 12.5 and later enables capturing from tape., so your version of iMovie and 12.5.1 should be good.

Do you have any other devices that could test out the integrity of the FireWire to Thunderbolt cable?

If your cable is good then if it worked before any updates /upgrades then it should work now.

Sometimes connecting the cables and dis-connecting then re-connecting the cables jogs iMovie to recognise.