big surcatalinamacosmojavesoftware-update
I have a Macbook air 2015 with 128 GB storage and I just upgraded from Yosemite to Mojave. Surprisingly, after upgrade to Mojave, the amount of storage I had left went from 36 to 46 GB.
So my question is, if I update to Catalina or Big Sur, will this free up even more space or will it consume more?
In your case, the Mac doesn’t meet the requirements for Big Sur. You did everything correct, except checking the supported hardware.
Allan has a good answer for overall relating to BigSur. Here's an answer for the specific make and model. According to Apple's website, there are a few models that supported Catalina that will not support BigSur (macOS 10.16/11).
The machines that support BigSur are:
Big Sur Preview (Apple's website) Navigate to near the bottom of the page to find compatibility information.
Cause any issues with iCloud Music and iCloud Photo libraries as I will use them on both macOS Catalina and macOS Big Sur?
No.
Jeopardize my Bootcamp partition in any way?
No.
Allow me to reclaim the space used by macOS Catalina currently so when I remove it I can allocate that space to macOS Big Sur?
No.
I would suggest one of the following two alternatives.
→Startup Disk… from the menu bar. Choose to restart from the replicated Catalina. This would be the one that is not initially highlighted. Use the Disk Utility to erase the APFS container partition with the original Catalina. Enter a name for the new APFS volume where Big Sur will be installed. Next, quit the Disk Utility and install Big Sur to the new APFS volume you just created. If necessary, first download Big Sur from the App Store. Later, you can remove the APFS container partition with the replicated Catalina and merge the space back into the APFS container partition with Big Sur.Any other issues?
No.
However, user user3439894 has suggested the following popup message could be an issue. This popup may occur when booting Mojave on a Mac with Mojave and Big Sur installed in either the same or different APFS containers.
Best Answer
Normally, one OS update replaces the file contents of the previous one. While there might be some small variation in size between OS versions, I would not expect an additional 10 GB to get used up.
However, some space will be needed to download the new OS installer before it is launched.
I would install the OS, and then check how much space you have. There are disk utilities like OmniDiskSweeper that sort your whole drive by size, showing you exactly what is taking up the space and letting you delete it, if that is advisable.
You may also want to check if you have any backups of iPhones or iPads saved to your Mac, as these can take up large amounts of space.