You would not be able to reinstall TurboTax for any year earlier than three years prior to the current year. As of now, you would not be able to reinstall any year earlier than 2021. But it is also very unlikely that you would have to amend any earlier year. It's too late to get a refund from an amended return for any year earlier than 2022, and the IRS does not audit tax returns more than three years old except in unusual circumstances.
As long as you have PDFs of the older tax returns, I would suggest that you can safely delete the software for 2020 and earlier. In the very unlikely event that you had to amend an earlier year, you, or a tax professional that you hire, could do it manually using downloaded forms.