I’ve forked this exchange off since it relates to fstrim - which differs from the KDE Plasma problem I’d posted earlier (thankfully solved by @Aragorn!)
The separate topic pertains to whether using fstrim on a Manjaro/High Sierra MacOS dual boot internal SSD was wise or safe given Mac’s own OS-based garbage collection protocols.
Although both operating systems reside on the same SSD, I do not believe that either partition is visible to the other - at least in default bootup mode.
So perhaps it comes down to whether the Arch Linux fstrim (and/or native MacOS garbage collection function) operate on the entire SSD, or on merely the partitions that are mounted and visible at the time of their respective cleanup execution. I dunno’.
Whether the OWC brand firmware self-trim function makes my use of fstrim-timer wise remains another unknown. But your point about once-a-week frequency not likely to cause much harm over the long run “feels” right to me too.
I’ve posted this in case someone with other knowledge and perspectives on some of the overlapping trim functions cares to weigh in. If it gets quiet, I’ll close this thread out to avoid creating “unsolved” posts.
Thanks again.