iOS only project contains My Mac as run destination

I've had a similar issue. What worked for me was setting:

SUPPORTED_PLATFORMS = "iphonesimulator iphoneos";

As well as setting:

SUPPORTS_MACCATALYST = NO;
DERIVE_MACCATALYST_PRODUCT_BUNDLE_IDENTIFIER = NO;

It did not work the first time, but it worked after I switched the Support Mac Catalyst option from NO to YES and back to NO again.

So the culprit turns out to be a test target that had SUPPORTS_MACCATALYST = YES. If just a single target in your project has SUPPORTS_MACCATALYST set to YES then My Mac will show up.