Import .tar file emails into Thunderbird

My overall intent is to get old emails that are in my Bluehost domain host into a Workspace/Gmail account. From what I've been able to learn, Workspace/Gmail will only allow importing from either Outlook or another Gmail account. So I exported the emails at Bluehost into a cur.tar folder, saved to my computer, and I created a new Gmail account devoted solely to these emails. Thunderbird is apparently required to get the emails imported from the cur.tar file into the new Gmail account. And that's where I'm stuck. I used the Tbird Import tool, chose 'Import from a File' > 'Import Backed-up Profile' > 'Choose zip file', and the cur.tar zip file is greyed out. I tried expanding that zip file, and it won't allow selecting anything in it. What am I doing wrong here? Is there a less complicated way to get old emails from Bluehost into Workspace/Gmail? Edit: A little thoughtful thought brought me to the best, simplest strategy: contact Google's Workspace support. They guided me through the migration process, and it's now done. Sorry for this post...I'd delete it if I could find a way...