mac - install error on Xcode 12.4

On an old mac, disk space is very limited.  I have only 12GB left.

Cleaned up some caches under  ~/Library/Cached/

32GB still failed to install...

... until  38 GB,  now start download Xcode

when download is done,  only 12 GB is left.

wait until file expanded and started installing, when done,   20 GB.

restart machine, same empty disk space.