It seems that in the previous version released by Apple of macOS 11.2.1 Big Sur there was hiding a problem that directly affected the installation file. This problem seems like it could lead to data loss from disk and Apple released a new version a few hours ago with the solution to the problem detected.
It is not clear if this ruling affected all macOS Big Sur users since many do not have automatic updates active, but if so, Apple has already released the renewed version of it to avoid failures.
The tweet from Mr. Macintosh shows us the build of this new version of macOS Big Sur 11.2.1 that in this case it is 20D75. This version is now available for official download for all users and fixes the problem that could cause data loss:
macOS Big Sur 11.2.1 (20D75) full installer is now available for download.
I've confirmed the new installer now checks for free space properly.
This was a serious problem, and I'm glad users will no longer get caught by this issue. https://t.co/dYSuRjdd4p pic.twitter.com/ILxoKfhORn
- Mr. Macintosh (@ClassicII_MrMac) February 15, 2021
It may be that some users who tried to install the previous version got a message of insufficient disk space to install. The process was stopped and could not be updated, now with the new version released is checked that there is enough storage space available before the installation begins and in this way the problem of accidentally deleting files is avoided.