I tend to think that McKayla, used for girls, is Michaela, but can't think of a justification for MacKenzie.
Surnames as first names have been used in Scotland for long time; traditionally it's family surnames, so a fair amount of Mac- . There are cases of MacKenzie as a first name for girls back to the 1880s, and probably even further as a middle name which might be the name in everyday use, but it didn't really take off until the late '80s/early '90s, around the same time it peaked for girls in the USA, where it was in the top 50 for a few years. I've never personally seen MacKayla (or MacKinna, which is also popular for girls in the USA) used as a first name or surname in Scotland. In general, Mac- first names aren't that prevalent - in the 2021 data only MacKenzie showed up on the list for girls (ranked 442 with 7 occurrences). For boys, Mac alone was the most popular (ranked 221 with 20 instances), then Mack (316/12), MacKenzie (401/8), and MacAulay (601/4).
Unless the name MacKinna has some more direct Irish roots, I'm guessing it's a take-off on MacKenna, from the old Gaelic surnames MacCionadha, or possibly MacCinidh (usually anglicised as MacKinnie). No idea re MacKayla - MacÀidh/MacAoidh, usually anglicised as MacKay, MacKee, or MacHugh, is the closest surname I can think of. MacDara probably would be perceived as feminine in this context too, by non-Irish (and non-Gaelic) speakers. I nominate MacAbhra/MacAra, MacAnndra, MacCàba, MacColla, MacNia, and MacRiada for the next generation of genuine Scottish "feminine son of" names... 😁🏴
Seriously, it is a bit strange to use "son of" for a girl, especially as the body of the name is most often a male first name. But in Scotland the female (Nic - daughter of) and neutral (Ua - child of) forms were mostly converted to Mac sometime in the sixteenth century, so Mac is a kind of default "child of" - no odder I suppose than naming a girl Addison, Madison or Carson. There are even some traditional Mac- names where the first name referenced is likely from the mother, like Mac a' Leòra/MacLabhra or MacClure (Laura) or MacSìle/MacSìleas (Cecilia/Sheila), but the etymology is hard to trace. MacAilis/MacAilish may be "son of Alice", but is also conflated with similar names like MacAulish and MacAuley.
Some Scottish Mac- names seem to come from an unnamed mother or female ancestor - for example MacCuinn, MacCuithein, MacShuibhne (and the anglicised MacQueen) have generally been interpreted as son/descendant of the queen, and MacCròin/MacCrone as son/descendant of the crone. And then there are traditional Mac names that don't refer to a specific person's first name, for example Mac a' Bhiocair/MacBhiocair/MacVicar = son of the vicar, Mac a' Chruiteir/MacWhirter = son of the harper, Mac a' Bhruthainn/MacBrayne = son of the brown one, Mac'IlleNaoimh/MacNiven = son of the saint, etc. I'd guess MacDara fits this pattern - something like son of oak/the oaks? These ones might, purely in terms of the meaning and if you read "son" as child/descendant, be a little less male-centred.
Thank you for coming to my MacTed Talk! 🤓😴