most don't seem to have two factor authentication

https://personal.vanguard.com/us/insights/article/security-codes-112015

If you sign up for this service—sometimes referred to as "two-step authentication" or "two-factor authentication"

https://support.robinhood.com/hc/en-us/articles/211546986-Two-Factor-Authentication

You can use two-factor authentication to add an extra layer of security to your account.

https://www.ml.com/privacy-and-security-center/our-people-and-our-policies.html

Once you enable this service online via the Security Center, we’ll send you a one-time code at each login based on your receipt preference.

all the major brokerages offer two factor if you want to use it if you are using the same log in and same password for everything i would suggest you may want to enable it with your brokerage!

however on that note if you have a lot of assets in a brokerage it is ususally in the brokerages best interest to keep you happy and they will take losses to keep you happy . so if i were you i would not worry too much other than making sure you have set up two factor!