for me, i'll find the closest arch to manjaro that simply does not rely on systemd
what you should do: delete that file and then listen to onlooker's advice about using apt to install software when you can
what is happening: an arbitrary file you create to hold the contents of some data you streamed off the internet, for very good reason, is not automatically treated as an executable, partly because for all wget knows, it's just a photograph or some text. to mark a file as executable, you need to run chmod +x /path/to/script/file to add to the file's permissions. to learn more, and you should, please learn about file permissions and how those work on linux systems.
looking at the code for btop it appears to just grab this information about memory usage out of /proc/meminfo directly, which you can cat yourself to look at. so if it's wrong, it seems likely that it's wrong because meminfo is mistaken in some way.
And on that note, I condemn in the harshest terms the response from communities like /r/linux on the subject. The vile harassment and hate directed at the FDO officer in question is obscene and completely unjustifiable. I don’t care what window manager or desktop environment you use – this kind of behavior is completely uncalled for. I expect better.
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no, i'm saying that i think there's got to be an archlinux that is similar to manjaro in terms of what is offered but differs in not having systemd. i have not done the research to determine what distros (if any) this describes.