Your machine will run the OS that followed Yosemite—MacOS 10.11 El Capitan— but even that is 4 years out of date now, and wouldn't change much. Apple provides security updates for the current OS, 10.15 Catalina, and the two previous versions, 10.14 and 10.13. In the fall, OS 10.16 Big Sur will be released, and 10.13 will be left behind. Let me know if you have any other questions. — The Mac Guy
Our Apple specialist is in Tuesday-Friday 8am to noon.
give them a call I c couldn't say
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