exu

This does not scale. I have 400 logins in my Bitwarden account right now.

You understood correctly. Seems like I missed some news on the syncing front.

Do you add separate keys on every device?
If you do, how long does it take you to add a new device?

A sufficiently strong password and additional TOTP should protect you well enough.

I'm thinking of phone recovery, where you're trying to get all your stuff back on a new device.
With a password manager, simply logging in will get you there and until passkeys can be synced automatically just like passwords this will need to be handled somehow.

Good incentive for the provider to fix it or go out of business.

QR codes are good 50% of the time; when you're trying to log in on a pc.
The reverse case is extremely annoying

I remain hopeful. Initially, when Keypass wanted to include a simple export option there was talk of banning them from using Passkeys.

Good, certificates should be automated anyways. Much more reliable than the once yearly outages because nobody renewed the thing or forgot some systems.

Surprisingly civil Phoronix comment section

I use migadu.com now, previously also used mailbox.org and protonmail.
The great part with migadu is how much control you have. Want to add multiple domains or have multiple users? No problem. (Though they reserve the right to ask what you're doing if it's excessive).
Limits are based on mails sent, mails received and storage space.
I was on their cheapest plan (19$/year) until I filled my receiving contingent because my servers had issues and monitoring kept dutifully sending email alerts about that.

Both, the browsers (and any other application) can choose to ignore your DNS settings and use whatever other mechanisms they like.