1) How can I share the fingerprint keys between chrome and safari?
You don't need to. That's not how it works. Chrome and Safari and every device will have a different key for the same service (see video)
2) How do I share keys between different types of devices? (mac, ios, android, windows)
You don't. You authenticate and a new key is created on each device, possibly on each piece of software (Firefox, Chrome, Safari, App). To be more clear, when and if you decide to use a service from a new device or new browser you'll be asked if you want to login via passkey. If you have a passkey on another device you can (see video) use that to login from the other device (similar to how google asks viat the gmail app of you were trying to log into some other device or Apple asks across your device). After you authenticate you can then create a new passkey for this device/software you're using. This new passkey is separate from the previous passkey. You effectively have 2 passkeys now, one to login with one device/software, one to with a different device/sofware. (See video)
3) What happens if my devices are gone?
You follow whatever recovery procedures the service has.
4) What happens if I want to change my login (email to a new email for example)?
Unrelated. Your email is not shared with passkey. So login and set a new email
5) Is account recovery handled simply by a reset-email?
That's up to the site/service just like it is without passkey
6) It seems a validation step of the email is missing?
That's up to the service as well. They could require an email but that's unrelated to passkey
1) How can I share the fingerprint keys between chrome and safari?
You don't need to. That's not how it works. Chrome and Safari and every device will have a different key for the same service (see video)
2) How do I share keys between different types of devices? (mac, ios, android, windows)
You don't. You authenticate and a new key is created on each device, possibly on each piece of software (Firefox, Chrome, Safari, App). To be more clear, when and if you decide to use a service from a new device or new browser you'll be asked if you want to login via passkey. If you have a passkey on another device you can (see video) use that to login from the other device (similar to how google asks viat the gmail app of you were trying to log into some other device or Apple asks across your device). After you authenticate you can then create a new passkey for this device/software you're using. This new passkey is separate from the previous passkey. You effectively have 2 passkeys now, one to login with one device/software, one to with a different device/sofware. (See video)
3) What happens if my devices are gone?
You follow whatever recovery procedures the service has.
4) What happens if I want to change my login (email to a new email for example)?
Unrelated. Your email is not shared with passkey. So login and set a new email
5) Is account recovery handled simply by a reset-email?
That's up to the site/service just like it is without passkey
6) It seems a validation step of the email is missing?
That's up to the service as well. They could require an email but that's unrelated to passkey