I've some questions about Ghidra released by NSA on Github. And research about it then saw a ycombinator thread for it. That answer was clever and funny.
As title marked, you really okay for just "open source" to trust it?
Only true if they can abuse the backdoor, if its tied to NSA infrastructure (which a competent backdoor would be), they couldn't use it. There is also precedence, the Germans didnt hesitate to publicise that Angela Merkel's phone was hacked, they could have used the malware to feed false information instead. Stuxnet was exposed to embarrass the US/Israel.
Cyber security companies would also have no qualms about publicising it. Finding a NSA backdoor would put them on the map, and they have no use for a backdoor.