How to install macOS Big Sur in a partition keeping Catalina as it is

Hello Parichay_Singhwani,

We understand you're trying to install macOS Big Sur, while still keeping macOS Catalina on a separate volume.

You can do this either by creating a second volume on your current hard drive or by using an external drive for the second volume. Prior to doing anything though, you'll want to be sure you have all your data on your Mac backed up. For help with backing up, check out: bak

Back up your Mac with Time Machine

Once your data is stored safely, you can begin to partition your Mac's hard drive to create a second volume for the second operating system. For help with doing so, please check out:

Partition a physical disk in Disk Utility on Mac

Once you've got the second volume set up, you can begin installing macOS Big Sur. To do so, download the Big Sur installer using your macOS Catalina partition, and choose the new volume when selecting where to install it. For more info, check out:

How to upgrade to macOS Big Sur

Once the install is complete, you can ensure you're booting to the correct volume by holding the Option key during startup of your Mac.

For more info on using Startup Manager or selecting which volume you want your Mac starting to, please review:

Change your Mac startup disk

We hope this information helps out! If you run into trouble along the way, just let us know.

Take care!

Best option is to create a new Volume in Disk Utility, not a partition.

Create a bootable USB installer of Big Sur and install Big Sur onto that new Volume.