I’ve been using KiCad since version 4, several years, on this same Mac.
I upgraded to 6 when the official release dropped. Before too long, I started noticing that saves on projects I was working on would take an appreciable amount of time (starting to approach a minute) even on relatively small things.
Recently being frustrated with it, I upgraded to 6.0.5 (after all 6.0.0 was sure to have some bugs, right? ).
Not only has the problem not gotten better, but it seems to be worse. I just opened it up and tried to switch from one project to another, and it basically pegged one CPU core and sat there spinning until I did a Force Quit. And projects I have opened since upgrading to 6.0.5 have the same issue of slow saves, both from PCBNew and from EESchema.
I did just upgrade “over the top of” the 6.0.0 version. I wouldn’t expect problems from that to manifest this way though.
I’m running Catalina, 10.15.7. I have some older software packages that are likely to break if I upgrade further, and as it is this is a very old macbook pro (mid-2012), but I have upgraded the memory (16G) and am running on an SSD (Catalina and beyond will not run at any speed on a hard drive). I have multiple other large apps I run routinely, for example Photoshop, which aren’t exhibiting this sort of problem.
I’ve by no means ruled out other issues with the laptop itself, but I wanted to just ping here and see if anyone else might be seeing anything similar. A cursory search here for performance mostly comes up with prior versions…