Big Sur Downloading issues

Hello everyone,

I'd so be grateful for any help you can give me on this.

I have tried downloading Big Sur three times, the fourth is underway whilst I type.

Ist attempt: At the last moment an error message flashed on and off so fast it did not give me time to read what the problem was.

2nd attempt: A message popped up saying that I did not have enough free space to complete the download when I have plenty of free space to spare.

3rd attempt: I have a message saying, 'The package Install Assistant.pkg fails to meet Gatekeeper policy' followed by, 'An error occurred while installing the selected updates'.

I am trying agin, as I said, but is there something I can do to facilitate the download that I've not done?

I'm confused.

I'm hoping someone more knowledgable than me will know something,

best wishes