Sorry, FNLT constraint = Finish No Later Than. Is this a project file you can share? It's impossible to tell what is going on without actually seeing the schedule. Can you "sanitize" the file replacing task names with 1,2,3 etc?

You may be able to get closer by using Autofilters on the Total Slack field. The definition in Project is tasks are critical if slack <=0. However, you could autofilter for tasks with slack less than 5 days (for example). You can also modify the default definition of critical in File > Options, Advanced.