Migrating NSF emails to Gmail or G-Suite can be tricky, especially if you dont have Lotus Notes installed on your system anymore. I faced the same situation and after exploring various options, I found that third-party solutions are the most straightforward. One that worked well for me was eSoftTools NSF to PST Converter. Surprisingly, even though it's named for PST conversion, it also supports exporting NSF files directly to Gmail.
The tool allows you to sign in with your Gmail credentials and transfer selected or entire mail folders. It doesnt require Lotus Notes installation, which is a huge plus for users like me who no longer have the app. It was pretty seamless and helped me get access to old work emails without much hassle.