https://youtu.be/NKIbR69opgc?si=kbp9mLaAZ5brQTxf

This is a nice little experiment to show you what happens when you try to parallel two inverters that are not synchronized. Just because the voltage matches does not mean they are in the same phase or synced up with their sine waves. You can also just look at the manual for any dedicated off-grid only solar inverter and they will make it very clear that you are not supposed to hook the output up to the mains panel and doing so will void your warranty and damage the unit. But I'm sure that those inverter manufacturers have no idea what they're talking about /s