In your circumstance, parked outside a restaurant on a busy road, an alarm like this might have been a deterrent:
https://amzn.to/3RnqRXC
I was pleasantly surprised to find that it's much better made than you'd think for the price, and after two years on the bike it's still doing fine. I have it strapped under the rear basket just above the rear fender, where it's invisible to potential thieves. Great range on the remote and is quite sensitive - nobody moves my bike even a little bit without first a warning blurt, then an ear-splitting siren if they're dumb enough to proceed. It's also possible to manually blurt it with the remote if you have eyes-on and don't want people too close. You can adjust the volume, sensitivity and the type of alarm sound, as I recall.
The only downside is that the batteries in the alarm itself only last one riding season. They're easy and cheap to replace in the spring, but I have to cut and then reinstall zipties - not a huge deal. The remote takes a bit of getting used to, as you arm/disarm with two separate buttons.
I use this alarm in addition to my Abus folding and/or U-lock when parking it out of my sight. Recommended, even if belatedly in your case.
https://amzn.to/3RnqRXC
I was pleasantly surprised to find that it's much better made than you'd think for the price, and after two years on the bike it's still doing fine. I have it strapped under the rear basket just above the rear fender, where it's invisible to potential thieves. Great range on the remote and is quite sensitive - nobody moves my bike even a little bit without first a warning blurt, then an ear-splitting siren if they're dumb enough to proceed. It's also possible to manually blurt it with the remote if you have eyes-on and don't want people too close. You can adjust the volume, sensitivity and the type of alarm sound, as I recall.
The only downside is that the batteries in the alarm itself only last one riding season. They're easy and cheap to replace in the spring, but I have to cut and then reinstall zipties - not a huge deal. The remote takes a bit of getting used to, as you arm/disarm with two separate buttons.
I use this alarm in addition to my Abus folding and/or U-lock when parking it out of my sight. Recommended, even if belatedly in your case.