LucyLovesMarvel McAfee isn't usually an issue, but any antivirus can act up suddenly and for no apparent reason. McAfee also isn't any better than Windows Defender in most cases. So if you don't particularly want to use it, here's how to remove it safely (the consumer product removal tool):
https://www.mcafee.com/support/s/article/000001616?language=en_US
65 MB isn't necessarily excessively large for a save, but it might be large enough to trigger the antivirus you're using to object. So if removing McAfee doesn't help, check Windows Defender's Controlled Folder Access settings (again, if you have already, since it might have disabled itself while McAfee was running) to make sure it's not blocking anything Sims 4-related.