I'm not looking to debate the merits of the concept. TP to me is just a tool like any other. It is often not what I want due to its effect on transients, but it is also sometimes exactly what I want for that exact same reason.

I'm looking for the most lightweight tool that can do the following. Assume in each case that the plugin in question has its threshold set at 0dbFs:

1) If a signal goes through where the peak and true peak values match with both at 0dBfs, then the plugs does NOTHING to the signal.

2) If a signal goes through that has been clipped, so the peak is at 0dBfs, but the TP is higher, then it does the absolute bare minimum transient rounding necessary to bring the TP down to match the peak at 0dBfs.

I've tried this with several limiters, and each ended up rounding down the signals that DIDN'T have TP above 0dBfs as well, and I'm looking for something that ONLY kicks in if there's a peak/tp mismatch.

If there are limiters (or such) with such behavior, then which is the absolute lightest for resource consumption?

I'm on m1 (soon to be m3) mac / Bitwig (vst3) if it matters

This sounds like a soft clipper, but you’d set the threshold below 0dB to get the behaviour.

A soft clipper would round an unclipped signal where the peak and TP are both hitting at 0dB, so it fails the first criteria.

It actually fails the second too since the soft knee without time considerations means that ALL values of 0dBfs are remapped lower. So it will round going into and out of the hard clip of a signal, but the hard clip will remain, and will now be below 0dBfs.

I'm getting very mixed results with TP limiters for their ability to do either. For instance, some just round everything too much while TDR's Limiter 6 with only the output module set to TP and the rest disabled seems to do the bare minimum rounding necessary to bring the TP much closer to the peak, BUT... it doesn't always keep the TP at zero, so the output has to sometimes be dialed back manually. I'm hoping to find something more reliable that does the least possible amount of damage in all cases, yet has an absolute (TP) ceiling.