Today is Monday, it won't let me by tickets for Friday. Is that normal?

That's normal, as most chains (Cinemark, AMC, etc.) update their schedule for the upcoming weekend on Wednesday or Thursday. The only time you'll see screen times posted in advance are for tentpole movies (like Black Panther, Avengers movies, Star Wars movies, etc.).

Sure is!!

The schedule is changed every Thursday night, so that is as far ahead as you can purchase a ticket, unless it is a highly anticipated film, they probably won't have anything available past Thursday.

Yup.

You may have to wait until it gets closer to the day you want to buy tickets. I would try again tomorrow.