Mac Os Mojave freezes

Alas. So much for the easy solution.

This list (https://www.macworld.co.uk/feature/mac-software/apps-work-macos-mojave-3678735/) might point you to some trouble spots among the big software contenders, but it's worth noting I have a pretty good spread of many of the apps listed there (CS5, Word 2011, etc), and none of them crash or burn, nor do they contribute to any slowdowns on my Air. The trouble I was having on my Mini appears to have been due entirely to a failing HD.

That is the next thing to check, by the way. Run Disk Utility on your drives and see if any of them report problems in the SMART status (bottom left of the table of info here):

If it says anything other than "Verified", you'll need to replace the drive soon.

In addition to that, run over your Mac with a fine-tooth comb. If there's any third-party stuff loading in your system menu, or anything loading under "Login Items" with your user account, make sure it's up to date. Also, older software that was not cleanly uninstalled might have left something behind that's interfering with your system now — though tracking that down might be extraordinarily difficult.

Some third-party apps require you to disable SIP (system integrity protection) to install and run. If you don't remember ever booting to recovery and entering this command in the Terminal:

csrutil disable

…then you probably don't have any such software on your machine. Nevertheless, try loading Terminal (you don't have to reboot to do this) and enter this command:

csrutil status

If you see anything other than "System Integrity Protection status: enabled.", you'll need to boot to recovery, select Terminal from the Utilities menu, and enter this command:

csrutil enable

…Followed by a reboot. You can only enable or disable SIP from recovery. You can't do it from safe boot or even via sudo.

Among other things, SIP keeps permissions on files and folders what they ought to be. If those permissions get munged, some programs (and possibly macOS itself) might have trouble functioning.

Do you have a third-party peripheral, such as a keyboard, mouse, printer, scanner, or some other hardware element? Confirm its drivers are up to date.

If you have Flash, make sure it's the most recent version. (Check it via the Flash Player item in System Preferences; if it's not there, you probably don't have Flash.) I got a system dialog today telling me the Flash updater daemon was 32-bit, not 64-bit, and so I needed to run an update (the default is for it to auto-update, but I turned that off years ago). Apps that have daemon programs like that, running in the background periodically, are likely suspects in quietly causing trouble in a largely-untraceable way.

Also, take a look at Font Book and see if there are any fonts listed that appear to be damaged or poorly coded. Problematic ones should show the yellow caution triangle next to them in the fonts list. Consider turning those off, or removing them, if there are any.

I've seen problems like software-extension incompatibility before, and it always results in unpredictable system performance somewhere. The trick always is finding out which program is the source of the problem. You've probably seen EtreCheck referenced in other posts in this forum. It might be worth running a report on your machine, seeing if there's anything noted in it, and removing the problematic software, if any.