I have a MacBook Air from 2015 which is on MacOS Mojave. When I go to update to Catalina my response is "this is not available at this time." The computer acts as if I have the most updated version. What should I do? It worked on another laptop

Finally worked. Doing as per the recommendation in comments before:

1. Run this command in the Terminal then reopen System Preferences > Software Update.

sudo softwareupdate --reset-ignored

2. Restart in safe mode, download and installed.

now I have the Catalina 10.15.4 :)

i will try all the functions.

thanks

Run this command in the Terminal then reopen System Preferences > Software Update.

sudo softwareupdate --reset-ignored

You're welcome. Make sure to delete any copy of "Install macOS Catalina" from the Applications folder if any, then try again while in Safe Mode.

How to use safe mode on your Mac - Apple Support

You need to upgrade, not update. You are trying to download the wrong file. See How to upgrade to macOS Catalina.

jessiemosquera wrote:

I have exactly the same issue

Same solution…

Run this command in the Terminal then reopen System Preferences > Software Update.

sudo softwareupdate --reset-ignored

Try this…

1. Restart your Mac and as soon as you hear the startup chime press the Shift key
2. Once the Apple logo shows and the progress bar starts, release the shift key.
3. It takes longer to get to the log in screen than normal.

SophieNora wrote:

how do I do that?

1. Copy the line that begins with sudo.
2. Run the Terminal app which is in the Applications > Utilities folder
3. Paste in the line into the Terminal then press Return
4. Type in your password and press return. You will not see the letters as you type.
5. Quit the Terminal
6. Reopen System Preferences > Software Updaate.

Thank you, it works..

I did it, now it shows me the Catalina, starts the download.. when it goes in 510Mb stops and says "the request is time out, An error occurred while installing the selected updates."

I have exactly the same issue

You should try the suggestion I made right above your last post using Safe Mode.