If you're worried about that kind of attack, once someone has access to your computer they can install a key logger. Better to get in the habit of locking your computer every time you stand up.
Apple Watch supports this - lock upon getting a certain distance from the device.
I believe 1Password also lets you lock itself after a period of time which can be very short.
I recommend adding a constant "PIN" you remember in your head to the end of each password in your password manager. It only takes a couple seconds to type it after the password manager auto-types the stronger, longer password.
I've never succeeded in explaining this to any password manager's tech support. They stay in business because their tools are convenient to use.
I've migrated from 1Password to a Dashlane family plan. I use two separate accounts for myself. I log in to one account to access sensitive financial sites, and log out explicitly before leaving my chair. I log into another account for everything else; do I care if my subscription to the Washington Post gets compromised? That account stays open for convenience.
Each password manager has a theory on how best to offer similar security/convenience with one account. None work as smoothly as having two accounts.