Unable to update MacBook Pro due to excess Macintosh HD data

"Macintosh HD - Data" is the drive volume that houses all of your user data. Everything. So it's no surprise that the bulk of your storage capacity is used there. This is normal and as it should be.

The erasure that Time Machine is prompting you to do is to the external drive that you want to back up to. It must be properly formatted for Time Machine's use. Time Machine prefers its own dedicated drive, so buy one to use now and in the future. Buy an external that is 2x-3x the total capacity of your Mac's startup drive. Trust me when I tell you that you will have a bad day when you'll wish you had done that.

FYI, 30 GB is not "plenty of storage". Plenty of storage is a minimum of 10%-15% of the startup drive's capacity at all times. What is the capacity of your startup drive?

I'm sure you know this, but once you have copied your photos, vids and large files to your external drive, you must delete those files from the internal drive to free up that disk space.

CleanMyMac is considered by many veteran users to be nothing more than malware itself. Many users discover CMM and similar anti-virus, cleaning, optimizing and VPN apps to be the source of problems that they experience. You'd be wise to uninstall that and don't look back. These apps are neither required nor recommended to be used on the Mac.

Since your goal here is to reclaim enough space to upgrade your computer, I'd suggest simply copying ALL of your files from the Desktop, Documents and Downloads folders onto your external drive and then deleting them from the startup disk. I'm confident that will free up a more than generous amount of drive space and let you get on with your upgrade. When that is accomplished you can copy the files from those folder back to your Mac's startup drive.

check the storage settings ,there might be lot of data in system data .

clear the cached files under user/library folder .