Apple Mail taken to the cloud.

I have a Mac Pro 2013 with Big Sur MacOS. I have been using my .mac email for a long time as my primary account and I was storing email on my macs going back to the late 1990's. Couple weeks ago I tried to send an email and it failed because it couldn't find an outbound server (sorry don't remember the exact error text). When I checked my accounts there were a couple old inactive mailboxes and iCloud. My apple Mail (IMAP) was not listed. So I clicked on the iCloud account and entered my apple credentials. I was then able to send the mail and see my inbox. I thought all was good.

Next day everyone on my Family Sharing is getting warnings that our 200GB iCloud drive is full. I monitor my family usage and know we were not close to full a few days before this incident. It appears to me that all the email I had been storing for decades on my Mac has been uploaded to iCloud drive.

Is there a way to get my email back and store it locally (I know thats old school, but the shoe fits)? I refuse to start paying $11/mo for apple email when I have terabytes of storage on my mac.

I'm also curious if this happened because of an macOS glitch or dumb delete accident on my part, or is it by design. Did Apple get rid of their IMAP service and now only lets you store email in iCloud to force you to pay a monthly fee for storage?