Not a virus, and not really an Avid issue either. A bad Google software update is writing over critical parts of the system, and here's the fix:
This problem showed up on Avid systems first, because Media Composer apparently requires users to disable SIP (System Integrity Protection) to install custom graphics drivers, and the update doesn't cause problems on Macs where SIP is active (it's on by default).
Yeah, there's been a ton of progress since FCP X 10.0. To answer your questions, yes FCP X can definitely handle 4K60 footage on a 4K24 timeline, and it's simple to play 60fps footage at 24fps — look for Automatic Speed in the Retime menu. The stabiliser in FCP X is reliable and fast, and there are third party options like Lock and Load too.
"However, Android devices can be a lot more powerful than Apple devices."
Really? Android has its strengths, and there are legitimate reasons to choose it over iOS, but not performance.
That PC doesn't include the iMac's 5K P3 monitor, and has 2x512GB (slow) SSDs instead of 1x2TB (very fast) SSD. Also, you don't have to buy RAM from Apple, as you can easily install your own third-party RAM in the 27" iMac. The price difference is really not as huge as stated.
The default shortcuts for this process in FCP X would be Command-B to blade at the playhead, and Option-[ to Trim Start, but ideally you'd want to remap them (as here) to two neighboring keys with no modifiers (e.g. F5, F6).
If your built-in keyer effect isn't good enough, look at Hawaiki Keyer. It's fantastic, and works with FCP X and Premiere.