Home button not working after replacement

eBay isn’t exactly the best source for replacement parts…the failure rates are higher than parts purchased through reputable vendors. That said, you logical approach makes sense. You tried a replacement HB and a replacement HB Link Flex. Assuming those parts are good, then the next step is to consider a logic board failure.

The issue here is that you are dealing with parts that could be defective themselves. Ideally, you need known-good parts or at least the confidence that the replacement parts are good. I wouldn’t have confidence in eBay parts myself because of the high failure rates, heck I don’t even have high confidence in the parts I source from big vendors ;>). For a professional repair tech, we usually have other devices laying around where we can confirm if replacement parts are good or not. It’s much harder for a DIY fixer that does one-offs.

As a last step, take a closer look at the condition of the replacement parts, especially the connectors and flex materials. They are easy to damage and even the slightest damage can cause issues so magnification is preferable. If everything looks good, then consider having a shop look at it.