Is it normal to say grace at thanksgiving?

We are secular family. But because it is an American holiday, we commemorate the first Thanksgiving from 1621 by reading this best guess

Elder William Brewster, who was a minister, said a prayer that went something like this: 'We thank God for our homes and our food and our safety in a new land. We thank God for the opportunity to create a new world for freedom and justice.’

(—ref ‘Charlie Brown Thanksgiving’)

I have an uncle who used to always nominate me for that duty.

Most religious people say grace at every meal

Absolutely.

Yes

Of course.