Okay, I am at my wit's end here. I feel like I have tried everything. Everything so far has failed spectacularly, which makes me realized how tall Google's garden walls are!

My Goal

I am getting rid of my gmail business account. It has 15 years of emails, about 500,000 emails which is about 200 GB. And I want to archive them before I delete the account. I am a Mac user, so my goal is to have an offline version using Apple Mail (On My Mac mailbox)

Tools

Google Business App gmail account
MacOS 15.6.1
Mac Mail.app
Thunderbird
(And 3 other computers)

Here's what I have tried

Attempt #1

Using Google Takeout, I tried taking-out all of my emails. After a few days and a 200 GB mbox from Google, I could not get it to import into either Mac's Mail.app or Thunderbird.

Attempt #2

I connected my gmail to MacMail and tried to download all 500K emails. BUT the connection to GMAIL would frequently fail. Sometimes it would lose connection for a few minutes...other times a few hours. Because I have so many custom settings on my mac, I thought that it might just be how locked down it was.

Attempt #3

I added my Gmail account to Thunderbird, but it too would periodically failed.

Attempts 4,5,6

Using my work desktop and my work laptop, I tried the same thing as attempt #2. But the connection between MacMail and Gmail was still losing its connection. I thought that maybe it was a Mac thing, so I tried a Linux laptop running Thunderbird. The connection still failed.

I called Google Support and they were blaming Apple....even though it failed on a Linux machine running Thunderbird.

Attempt 7

Two years ago, I had a good experience with Fastmail and migrating a Gmail account, so I upped my storage and used their migration tool. A few days later, all 500K emails seemed to be in my Fastmail account.

I then hooked up my Mac Mail.app to Fastmail, and 2 days later, all the emails seemed to have downloaded....BUT when I copied all the folders from FASTMAIL to a local mail folder "ON MY MAC", it seemed that some of the email bodies were blank.

Attempt 8

I went back to Google Takeout, and I tried exporting just a few "Labels" worth of emails. Two days later, I got the link, downloaded it, and I could not get the mbox to import into Mail (it crashed it) multiple times.

Attempt 9

I went back to the basics. Connected GMAIL to Mac's Mail.app. Let it download for two days. But I was still seeing the issue where some emails had blank bodies or images/attachments that were missing. If I clicked on an email, let it load, it would download the attachment.

So I would go through and click an email, wait 10-20 seconds for the images/attachments to load, and repeat that for the 50-100 emails in my test folders. Once every email seemed to be downloaded, I would copy that "label's" folder to my "ON MY MAC" folder. BUT alas, some of them still had blank bodies. After waiting an hour or two, then seemingly the emails I have copied over to my "On My Mac" have the attachments. But this is no solution, right? I can't click on 500K worth of emails individually. [Especially because a lot of them have multiple labels, which could mean a million or more clicks? F that!]

tldr

I need some outside the box thinking on how to get 500K emails out of a Gmail account and on to a local only folder in Mac Mail.app