Still doesn’t explain why you want to use TAS during flight. Those POH tables are solely for flight planning purposes, you don’t use that to set cruise power as you stated earlier.
You set the cruise power as described in the POH which will result more or less in the TAS from the table, you can use this together with wind data to determine groundspeed and therefore time and fuel required for flight. You are not supposed to adjust the cruise power depending on the TAS achieved.
In other words it doesn’t have much practical purpose in flight, its meant to be used for flight planning purposes. I don’t recall ever using TAS in flight, inflight performance tables are often in IAS/CAS, TAS is merely an intermediate step in calculating the groundspeed (which is directly displayed anyway).
I’m not 100% familiar with the TBM. Besides a Vmo, does it also have a Mmo described? I have flown turboprops with both a Vmo and Mmo limit, in which case MACH indication makes perfect sense…