When I click the tfm website from google "Your connection is not private
Attackers might be trying to steal your information from www.transformice.com (for example, passwords, messages, or credit cards). Learn more
NET::ERR_CERT_DATE_INVALID" comes up. I don't know if this is normal, but it really freaks me out??

I don't know about Chrome, but in Firefox you should click on "Advanced.." then "Accept the Risk and Continue".
Seems like an expired certificate.

edit: Yes, it's an expired certificate. Don't worry, it's normal:

a dit :

Websites prove their identity via certificates, which are valid for a set time period. The certificate for www.transformice.com expired on July 27, 2019.

chromebook is doing this to everyone you'll just have to use steam or stand alone

The SSL certificate (which has been causing this problem) has been renewed, you should no longer experience this issue.

In the future, you can post issues with connecting to the game here. Thank you!