Using Thunderbird, create a new local mail account. Connect to your gmail account using IMAP. Drag & drop your emails from the original account to your local

Using Thunderbird, create a new local mail account. Connect to your gmail account using IMAP. Drag & drop your emails from the original account to your local mailbox in Thunderbird. This process may require a little bit of babysitting, or work flawlessly without a hitch, I've seen both outcomes doing this for folks over the years.