Tennessee's public universities don't have a single, universal ACT score requirement. Each university and even individual programs within a university will have its own admissions standards. Some may be test-optional, meaning they don't require an ACT score at all. Others will have minimum scores, and some may even consider the ACT score heavily in their admissions decisions.
To find the specific ACT score requirements (or lack thereof), you must check the admissions requirements for each individual Tennessee university and program you're interested in applying to. Their websites will have this information.