I largely agree - a password manager is the best solution.
I chose Lastpass - it is cross platform and I don't have to worry about database management - the DB is in their cloud (encrypted with a key they don'y know).

Adding two factor authentication (2FA) for the most critical sited (gmail, lastpass, bank, etc) is IMO mandatory an excellent layer of added security with a minimum of hassle. Most sites only ask for 2FA if you are on a new device or once a month or so.

As to your “Key file / provider” - you might want to consider using a USB security key, like Yubikey. That removes the vulnerability you have by having your key permanently on your SSD - if it is on your SSD is can be copied by others if your devices is hacked or stolen. The data on a USB security key, on the other hand, cannot be copied. And if it stolen, you will know it. I keep my with my house/car keys and the keyring.

Finally, I relly look forward to when Webauthn becomes widespread - perhaps removing need for passwords.