Why won't macOS Catalina install on my Mac?This problem begins with the introduction of many users with macOS Catalina. And although the result of all, faced with it, one, causing its causes may be very different.
Firstly, the macOS Catalina download may stop due to the lack of disk space, because the update requires at least 6 GB if you upgrade from Mojave or 23 GB from High Sierra. Therefore, before starting the update we recommend to make sure that there is free space.
If the shortage became known during the installation, restart your Mac and press Control + R to enter the recovery menu, select Disk boot, then delete unnecessary files from the memory, and repeat the installation.
Secondly, the inability to complete the download may occur due to the disconnection of the connection with Wi-Fi. To avoid this, it is recommended either to locate the upgraded computer in the immediate vicinity of the router, or to connect to the Network directly via Ethernet.
If problems arise when installing an update located on an external drive via an adapter, try connecting it directly to the Thunderbolt port, or use another adapter. Perhaps this bandwidth was not enough.
Unfortunately, problems are far from uncommon for most updates, but almost every one of them can be solved. The main thing is to know what manipulations should be made in order to restore the Mac to its former stability.