The NSA, the original primary developer of SELinux, released the first version to the open source development community under the GNU GPL on December 22, 2000.[6] The software was merged into the mainline Linux kernel 2.6.0-test3, released on 8 August 2003. Other significant contributors include Red Hat, Network Associates, Secure Computing Corporation, Tresys Technology, and Trusted Computer Solutions.
The NSA has a “Technology Transfer Program”, where they actually have published a lot of (actually great) software to the public. SELinux and Ghidra are popular - and there are quite a few more: https://code.nsa.gov/
Apache NiFi is something I used in the past, and it was actually really neat to work with.
And seriously, taking caution after the recent OSS drama is fine, but SELinux is probably one of the most scrutinized pieces of code. Chances are extremely high that a state actor such as the NSA has either absolutely zero interest in what you’re doing, or should you be interesting for the NSA - godspeed, they probably have better ways of fucking you over than elaborate year-long OSS backdooring.