the INS dsrtk does not follow the great circle path and instead stays on the initial track calculated at the from waypoint (this may or may not be the same problem as AP in INS is offset in 1.0.7 - Systems - iniBuilds Forum)

the aircraft is flying between NZCH (43°29.4‘S 172°32.1E) and AN07/AT07 (69°26.2S 076°19.0E), these are the only 2 waypoints loaded in the INS, a 3121nmi leg. DSRTK stays at 207.9 the entire way, which also shows on the HSI

the aircraft also deviates from the track continuously, maybe if DSRTK is fixed this problem will go away on its own as i'm guessing the INS uses DSRTK as a reference and adds corrections (may or may not be limited to 45°, aircraft may eventually fly a straight heading given long enough leg) on top of it based on crosstrack deviation

track on TK/GS and heading on HDG/DA is the same number (this should only be the case when below 75kt groundspeed)

drift angle seems to be the difference between heading and DSRTK, it should be the difference between heading and track

and a question on the displayed XTK, the manual says the LTN72 displays the XTK offset set by the crew, are you guys sure that's true? because on CIVA units it displays crosstrack distance to current leg (outputs to HSI deviation)

Try again in 1.0.8 update and let us know please.

Usage of Greater Circle distances is one of the updated items.