The CLI has more functionality than the API, so you might have better luck listing all entries that way then looping through the details of each entry if the list doesn't contain the datetime.

If the exported Json contains dates, its easy to write a simple python/any language script to sort it accordingly

I remember using that Lastpass feature years ago and it never worked except for like 5 popular sites.

Do not upload your passwords to LastPass. I'm serious.

I used to be on LP, but they've had so many security breaches they've lost all trust.

I think you’re either stuck writing a custom script or uploading to an online service that can do the mass update, then back out all your data. I had lastpass then ditched them after the breach when they didn’t clearly communicate user impact. The auto change password functionality was hit or miss for me, so if you go this route make sure you get the functionality you need from a company you can trust.

Though if you do this once with strong unique passwords, you shouldn’t have to do a mass update again, right?

Keepass works great and you can use syncthing to keep up to date keyfiles on all your devices. I use keepassxc on PC and keepassdx on mobile.

KeePass.