Today's broadcast standard is EBU-R103 and basically all stations require files to be complaint with it.
Resolve broadcast safe option has nothing to do with it as it's outdated and based on IRE and designed for analog signal. It should be removed.
This has been discussed many times.
Read stories from this forum were people have files rejected after ticking this useless box in Resolve
You need to keep signal within limited range (+ gamut needs to be respected, but Resolve will do it for you). There are thresholds which signal is allowed to go outside (eg. 20–984 in DPP spec), but you will get overshoots moment you use any compression, so you want to stay within ideal levels during grading. Threshold were designed to cover those overshoots not to purposely go outside levels during grading.
If you don't touch retain super b/w you have guarantee no data will be outside ideal levels and even if you get overshoot due to compression you will be covered by thresholds. R103 has been designed this way on purpose.
If you use retain super white/blacks you have basically guarantee that files will be rejected purely on fact that they may have super w/b data, which for broadcast is big no go (even if it's not causing any issues).
TVs behaviour is meaningless here. Properly set TV will show black for YUV signal at 64 and this is your reference point (regardless if there is a super black displayed or not).
Resolve manual is not a guide how to deliver files to broadcast. It doesn't even cover that well all Resolve own features