the idea is: if we do find life elsewhere, especially basic life, it suggests that getting to that stage isn't super rare. which means the great filter probably isn't behind us (like abiogenesis or single-cell to multi-cell jump), but possibly ahead of us - maybe in surviving long-term, avoiding self-destruction, spreading beyond one planet, etc.
finding life doesn't eliminate the great filter - it raises the unsettling possibility that we haven't hit it yet.
The argument you're referencing is usually about finding life on a nearby planet, e.g. on Mars. Nick Bostrom has articulated [0] this argument. But finding life on a distant planet lacks the same statistical power for instilling this existential fear.
Of course. It'd be much worse if we found life on Mars than on a distant planet. In either case, the chances of humanity being ahead of the "great filter" are greatly reduced.
finding life doesn't eliminate the great filter - it raises the unsettling possibility that we haven't hit it yet.