Just installed latest Strawberry for Windows, and noticed exporting as M3U allowed typing in .m3u8 as extension name when saving.
My main reason for posting this in the first place, was cause I seemed to recall that for whatever reason I couldn't type in .m3u8 as extension when exporting in M3U format, in my Ubuntu installation.. Uh, man, I can't really trust my memories these days..
High CPU usage on Mac is due to a macOS-specific QT5 problem with the Track/Playlist screen and scrolling/interacting with it when on a high resolution display (such as your Retina screen on your MacBook) - you should find that CPU usage will drop and performance will noticeably improve if you resize your Strawberry window to something very small.
I did have an issue ticket raised on this issue on the Strawberry GitHub page, which was closed as it was deemed to be unresolvable under QT5, and I'm trying to get it reopened/looked at again, now that QT6 has been released (which may have a fix for this CPU usage/performance issue).
It's not possible through configuration.
But it should be possible to change in the code if you want to compile by source.
I think all you need to do is to change the following line in src/collectionmodel.cpp
@sylvia The generalization of this is font-size control. I would welcome an option for such but for the opposite reason - to make the size smaller. And while dealing with the appearance of the playlist I suggest also options for the padding on the text and the background color of the alternating lines.