Yes, you can install QuickBooks Desktop for Mac 2021 R15 on your MacBook Air for a test run, @Rookie24.

To begin with, QuickBooks Desktop for Mac typically allows installation on up to two computers, provided both are used by the same individual and not simultaneously. This means you can install the R15 version on your MacBook Air running macOS Sequoia 15.6 without deactivating or registering the copy on your iMac.

However, please note that QuickBooks Desktop for Mac 2021 is a discontinued version, and QuickBooks has not released updates for compatibility with macOS Sequoia 15.6. With this, you may encounter compatibility issues. For this reason, you can either use a newer version of QuickBooks for Mac to match the compatibility or, before upgrading your iMac, it's wise to treat your MacBook Air test run as a dry run. If the test run is successful, you can upgrade your iMac and continue using QuickBooks there as your primary system.

You've been a loyal customer for 30 years and you deserve a smooth experience. If you need help preparing for your iMac upgrade or want to explore backup options, we're here to help.