Is there a way to get mail to look like the legacy versions in Monterey?

Show us a screenshot of what you're seeing. I use the two 3 pane setup: sidebar on left, list of emails in the center and the selected email on the right.

I use the Dark Mode so there's quite a contrast of the white text against the black background. I also set the font to the following and have no problems viewing emails or the list of emails:

What are the "legacy versions." To me, it looks pretty much the same as it has for at least five years. I don't really remember what might be called a legacy version besides being stuck looking at a bunch of columns of info I don't care about.

If you want columns, you can turn that on from the View menu.

Can you describe the problem in more specific, objective terms? No one here know what previous version of macOS you were running or how it appeared on your screen. There could be multiple issues that change the appearance. If you specifically list what you are seeing, how you don't like it, and how you would like it to be different, for each issue, I'm sure we could help.