Will Adobe Muse work with Apple Mac OS 10.15.3 You have mentioned that it possibly will not be updated for Mac system updates.
Muse 18.1 works on Catalina. But Muse has reached its end of life. Support for Muse officially ends in a few days. Are you sure you want to keep using Muse?
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Adobe stopped offering Muse as a single app after the EOL was announced. The only way you can get Muse now is as a legacy product with a paid Creative Cloud All Apps plan. Adobe doesn't promote Muse at all. And after March 26 when support ends, it's unclear if Muse will still be available from CC Desktop or not. There's been no official word on that yet.