I believe the issues is viruses. Malicious people are more than willing to exploit any opening they can. Microsoft has moved on and won't fix any newly found security risks on old platforms.
You're probably fine. Just don't put any credit cards, home address info, etc onto this machine. Maybe all that data is fine, if contained inside the web browser only? I'm not sure what security Chrome Edge etc have for preventing data from being stolen.
Nonsense. I use win7 constantly with all my sensitive information.
You have it backwards. All that info is fine if it isn't in the browser. In the browser is the same vulnerability no matter what OS you use, unless the issue is you have to use a very old browser because the newer versions won't run on your OS.
It's all a bit silly. The personal info, banking, etc, unless you make some user error that gets you infected with something, the OS is just a means to run an app that sends encrypted data between two points.
Read the vulnerability lists carefully then decide if they affect you, before declaring that the sky is falling.
I'm not suggesting that it's impossible to be compromised due to some older OS flaw, but am suggesting that if you take the attitude that the OS is the answer, that you are ignoring the bigger picture and probably more likely at risk if OS is the supposed solution instead of the same safe computing practices no matter what OS is used.