Need Solution for Automated Notifications

Hello All,

Happy St. Patrick's Day!  I have a group of people that I need to remind to sign in to a website every 30 days after their last sign-in.  I thought I had this all vetted out, but now after I've rolled out the new process, I've noticed one hiccup: 

I have a formula checkbox that will automatically check itself when today's date is 30 days after their last sign-in date.  This is supposed to trigger a modification notification that then sends them an email with instructions to sign back in.  However, the formula checkbox doesn't actually count as "modifying" the record.  So, I have to do this manually until I can figure out a fix.  Any ideas? 

I was thinking I could possibly create a pipeline that modifies a new field -- let's call it "today" date field -- on a daily basis, which I'm hoping would trigger the email to be sent.  Anyone have any insight or a similar experience they can relate to?