To replicate, you must have an icloud account that uses hardware key as 2FA. The following is the expected behavior

1. Open browser and go to https://icloud.com.
2. Log into your Apple account.
3. The site will prompt you to press the button on the hardware key and also prompt you for the hardware key's PIN. 
4. User enter the PIN and the browser logs you into the apple account.

However, if the enpass extension is installed, step 3 does not prompt for the pin and there is a spinning progress circle that never goes away. It is definitely the enpass extension, since removing it allows it to work. The following are the configuration

Platform: Apple M1, MacOS Sonoma 14.5
Enpass desktop version: 6.11.0
Enpass Extension version: 6.9.4.1

I've reported this issue to the Enpass technical team. They are currently investigating it, and I will reach out to you with updates as soon as I receive them. 

#SI-3970

Update, I replicated this issue under ChromeOS and Chrome browser. Just to make sure the problem is understood. When you log into icloud, a prompt for the hardware key appears and then you press the hardware key to login. When enpass browser extension is enable, the iCloud popup for hardware key will not appear and you won't be able to login. If you disable the enpass extension, the issue goes away. The browser extension appears to prevent the hardware key popup.

I am reporting that the latest extension 6.11.0 fixed the issue on Chrome on ChromeOS, and firefox on MacOS and Linux. What change is when you click on continue to the 2FA prompt, you get a prompt to press the hardware key button. Previously, the popup never appear and you get stuck. I like to thank the enpass team in fixing this issue. I will report this to the firefox forum.