Error: "Oops, something went wrong while loading" [SEE APPROVED ANSWER]

Now fixed for me. I removed the extensions from both Chrome and Edge. I also deleted the 1Password for Safari app from my Applications folder. I then restarted my MacBook Pro. Once it restarted, I reinstalled the browser extension for both Chrome and Edge. I also re-downloaded 1Passsord for Safari from the Mac App Store. After that, we’ll three browsers worked fine with 1Password.

I'll get onto the suggested fixes shortly, but just wanted to float an idea here.
It seems we've got a 'friendly' crowd here, 1Password. Perhaps consider something like an 'insiders' release. That way, us friendlies can do a first round real world test for you before releasing into the wild. I've got a family subscription and 1Password is my elderly mother's lifeline. When things like this happens, it takes a lot of effort to get her processes aligned again, including having to explain why the known process doesn't work anymore.
Just a thought...

Just cleared issue on my device.
I am using Safari on Mac OS Ventura.
I followed the support team recommendation for Safari in Mac OS Ventura. And only did the steps mentioned below. ( https://support.1password.com/connect-1password-browser-app/#if-youre-using-macos-ventura-or-later ) Scroll down to ‘If you are using Mac OS Ventura or later’.
I went into Mac System Settings> General> Allow in the background. I saw that I had 1 Password 7 and 8 enabled. I disabled 1Password 7 and the trouble vanished and the plug-in appears to now be fully functional. 1 Password 8.10.9 and plugin 2.14.0. (1 Password 7 may have been installed during my earlier troubleshooting steps)

Another 28 hours have passed, another three or four cycles of uninstalls and reinstalls. 1Password for Safari is still not working for me. In contrast to most of the comments here, I don't see any hint of the existence of 1Password within Safari. It does not appear in Preferences, nor does its icon appear at the top of any Safari browser window, where it has always been visible before. 1Password for Safari 2.14.0 is in my Applications folder. I have deleted it and reinstalled it many times. I'm using 8.10.9 for Mac, on MacOS 12.6.8, with all updates. Safari 16.6. Deleting 2.14.0 and installing 2.13.0 from a backup also didn't solve the problem for me.

My above solution only lasted for about 30 minutes and the trouble returned. I then followed ag_tommy APPROVED ANSWER above and everything is working again other than you have to enter your Master Password manually.

I'm experiencing something similar with 2.14.0

After upgrading the entire 1password system is up the wazoo. Can't get anything to fill in anywhere in Safari. Downgrading to 2.13.0 (Copying the app from another Mac) restores full functionality.

Unusual for your guys to break things this badly.

This is a follow-up to my previous comments. I've restarted my computer another ten times, working on troubleshooting a different problem. Finally, and suddenly, 1Password for Safari appeared in my Safari > Preferences > Extensions. I checked the box, and at last, I have 1Password working again in Safari. The extension that is working is the old one, 2.13.0, which I reinstalled earlier today from a backup.

I'm having the exact same problem as mscheurer. 1Password is entirely non-functional in Safari.

A comment that I placed here a few hours ago has disappeared. Curious. I have been able to get 1Password for Safari working again, by deleting version 2.14.0, and installing 2.13.0 from a backup. It did not work immediately. Restarting Safari and restarting my computer didn't solve the problem. I still could not see 1Password for Safari in the Safari Preferences > Extensions. However, after about ten restarts while troubleshooting another problem, 1Password for Safari did finally appear in Safari Preferences. I was then able to check its checkbox, and version 2.13.0 has been working for me since then.

I have the same error.

Unfortunately, the 1st part of ag_tommy didn't work.

Please try turning off the extension and turning it on again:
* Right-click the 1Password icon in your browser's toolbar and click "Manage Extension."
* Turn off the 1Password extension and then turn it back on again.
* Click on the 1Password extension in your browser's toolbar.

Björn