The answer to 'why is my mini split blowing hot air' is that your mini split system may be in the wrong mode or have a mechanical issue. Mini splits are heat pump systems that can provide both heating and cooling, but sometimes they can get stuck in the wrong mode or have a problem that causes them to blow hot air when you want cool air.
Some common causes include a thermostat issue, refrigerant leak, compressor failure, or problem with the reversing valve that switches between heating and cooling. You'll want to check the system settings and do some basic troubleshooting, but if the issue persists, it's best to call in an HVAC professional to properly diagnose and repair the problem.