Whoa, nice project! Way an overkill, both for my use (i not "play" too much with electronics, not much as years ago, i repair sometimes something for my use), and an overkill for testing a chinesium igbt 😅
In any case, i've found something nice to read about. It's an argument that i've never explored.
For the repair process, luckily it have an optoisolated driver (A3120) and only few components on the gate, already all measured. Had to replace a resistor and both the drivers. Also found some failed semiconductors and electrolitic caps on other boards. I not know the past of this ups, i've bought it time ago quite cheap as used/working, but never tested. In this days i've tested it, and got the surprise. It's identical to one that i already own, it's a "backup" unit in case mine stop working. The working one is also a repaired item, that had way less damage on it. They use the same battery, that is an home made lfp package... They are 5000va units, i have all the sensitive loads of the house protected, and also the well water pump (so that i not risk water in the basement in case of blackout).