Missing Partition

Hello chikitin,

Thank you for reaching out to Apple Support Communities.

Let's boot into recovery mode and attempt to run First Aid on your Disk:

"Open Disk Utility

In general, you can just open Disk Utility from the Utilities folder of your Applications folder. However, if your Mac doesn't start up all the way, or you want to repair the disk your Mac starts up from, open Disk Utility from macOS Recovery:

1. Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

• Apple silicon: Turn on your Mac and continue to press and hold the power button until you see the startup options window. Click the gear icon labeled Options, then click Continue.
• Intel processor: Turn on your Mac, then immediately press and hold these two keys until you see an Apple logo or other image: Command (⌘) and R.

2.You may be asked to select a user you know the password for. Select the user, then click Next and enter their administrator password.

3.From the utilities window in macOS Recovery, select Disk Utility and click Continue."

More details can be found here: How to repair a Mac disk with Disk Utility

If the issue persists, can you provide a few more details. What format is regular in? Also, is it recognized by any other OS versions?

Cheers!