If it is required by competitions or universities, it should be regarded as a polar molecule. You can draw a regular tetrahedron with the middle carbon as the center.
If the center is intermediate carbon, the endpoints of tetrahedron are H, H, CH3 and CH3, respectively. Because the two CH3 (methyl) groups are inclined to one side anyway, that is, their included angle is about 109 degrees and 28 minutes (of course, there will be deviations), which is far less than 180 degrees. Therefore, the repulsion of electron pairs by two methyl groups cannot cancel each other out. The same is true for two H atoms. Because of structural asymmetry, propane is polar.
By the way, propane does not have the same kind of isomers. When drawing, only any two endpoints are taken for analysis.
It should be pointed out that even though propane is considered polar, its polarity is very weak. Don't think about general problems.