The number of mentions of the name "Nintendo Switch" are extremely small (2), compared to the number of references to the console's codename (NX64). Some elements were ported and adjusted for the NX64, but nothing concrete that the game would be running on ARM.
The RAGE ENGINE was ported to ARM64 with the release of Red Dead Redemption 1 for the Nintendo Switch. As GTA 5 runs on top of the RAGE ENGINE, it would be a waste of time to try running GTA 5 on the Switch before the Engine itself. More references were found to Stadia (YETI) (x86) than the name "Nintendo Switch".
Any post claiming that GTA 5 was or is in development for the Nintendo Switch is completely based on hopium.
If the mention of a platform name in the source code meant that the game was in development for that platform, GTA 5 was in development for the Macintosh.