Any GMAIL alternatives preferably with an early internet like ui?

I don't know of any emails around who use an old-ui, but you could probably find browser extensions that allow you to edit the site's code so you can get a custom old-ui design. Technically Guerrilla Mail fits the bill but that's only a temporary email.

Post this question on redit maybe people will know!

Hello Kittys website used to offer email. I think they still do. There's a lot of niche email servers. What are your interests?

https://www.mail.com

Could probably use an email client and make it look old depending on the OS.
Linux with XFCE can be modified to look like Win9x with Chicago95, which would include the window for the email client.

I was about to say that you could choose the "go to old version" setting in the menu until i realised that they simply got rid of that feature. I guess the least you could do is make the emails compact and hide the chat and taskbar or whatever until you find an alternative, but what I normally do (although it really only works mostly on mobile devices for obvious reasons) is I use the mobile version of the site since it looks older at least somewhat, like it's sorta gettin there y'know?

Maybe:

https://squirrelmail.org/about/

My country has an email provider that has an "outdated but slightly modern" look. But I think it only works in my country... and it has to do with toads. lol

im sure with the wayback machine, you could get an old copy of mozilla thunderbird.