Is this a virus, why is page pop as I was watching videos as well

You probably have a subscribed calendar, or a push notification.

Those calendar subscriptions and push notifications are offered by various websites, and—if accepted—they then tend to age out and show TLS-related errors when the domain expires.

Remove the (usually unrecognized) subscribed calendar from your subscribed calendars:

Delete spam calendars and events on iPhone - Apple Support

Most folks encountering this probably don’t have any subscribed calendars.

For the removal of push notifications, see the above reply.

What happens when you click the "Details" on the error popup message (See the Pic below)

Best would be to Delete and Add the email account that is creating the issue.

You may also try changing SSL settings

Settings > Password & Accounts > [Select the Mail account} > [Tape on Account with the email ID} > Advanced > SSL Settings > [Disable]

Click <Account (in Blue)

Click on DONE (in Blue) when exiting in the previous screen

allowandgo is yet another push notification nuisance. You either tapped something on a site you visited to allow the notifications, or the site added itself, which is allowed by the OS.

Go to System > Notifications. If Safari is listed, change the notification settings to off.

Those calendar subscriptions and push notifications are offered by various websites, and—if accepted—they then tend to age out and show TLS-related errors when the domain expires.

That explains why when you try and go to that site, it loads (so to speak), but all you get is a blank page. Basically, the same tactic as spammers beating a spoofed email address to death for a few days, and then changing to a different one before it gets blacklisted.