Resize/Upscale questions

[Selur]

It means that 1150:1053 values have to be entered in to Input PAR and override default value of 1:1, correct?

If that PAR fixes the perspective: yes

One thing to clarify:
My video file is 720x576, DAR 4:3, Hybrid Video properties show PAR 1, as you explained:
“And a PAR of 1 would mean that the DAR is the same as the SAR (=sample aspect ration = 720/576).”

How this can be DAR = SAR. DAR is 4:3 = 1.333, SAR 720/576 = 1.25, they are not the same?

That was under the assumption that the Vapoursynth preview is shown correctly, which we now know that it wasn't.

Hybrid takes the PAR from the source. If there are no flags, the default flag for PAR is 1:1, so Hybrid assumes that.
(Since PAR defaults to 1:1 you get that DAR = SAR.)

Cu Selur