For the Mac, there's a 32 bit version of Kontakt through 5.5.2 and 64 bit versions beginning 5.6.1. Unlike Windows, there's no 32/64 bit version. Officially, Kontakt 5 is not supposed to work over Catalina and later but there are reports that 5.8.1 might—it's not supported, however.

If 5.8.1 doesn't work and you require the paid version of Kontakt, you'll have to upgrade, currently to Kontakt 7. If using the free Kontakt Player, that upgrade is free of course.

Since Kontakt Player is free and there's a free Factory Library, it's easy to test at no cost.

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Yes. You need to be a lot more specific about what's going on.

https://makemusic.zendesk.com/hc/en-us/community/posts/215729367-General-Discussion-House-Rules 

Kontakt 6 & 7  work fine over Big Sur and with Finale 27. Kontakt 5.whatever isn't enough information. Likewise, Big Sur isn't enough info either. Officially, 5.8.1 it is not supported by Native Instruments but there are many reports of people getting it working (over Monterey on my iMac Pro but I also kave 6 and 7). Please tell us what we need to know. I've already told you what I know with the information that you have shared.

Thank you very very much for your suggestion!

I will try it, but the main problem is my Finale wont load anyway most of my players and stand alone audio plugins. The only ones it can load are the "Uvi Workstation", "Opus" Player and of course "Aria".  All others just dont function. Do you have any suggestion on that ?