how to login when apple TV 1st gen won't recognise my password and/or id?

If your Apple TV box is black and 3.9 inches (9.9 cm) wide, then it is 2nd generation or later.

If you have an Apple TV (2nd or 3rd generation) and two-factor authentication for your Apple ID, then you may be asked to type your password followed by the six-digit verification code directly into the password field. Additionally, there is a time limit, after which the code becomes invalid.

Try this: First enter the characters of your password (do not submit yet), then manually request a new verification code, then append that code to the password (no spaces or other separating characters), and then submit. That should help you get passed the time limit.

It’s a white one and is 1st generation

That model unfortunately is no longer supported for the iTunes Store (since May 2018), which was the only remaining online service that required signing in to.

That model is not supported for syncing through later versions of the iTunes application (since v12.6.3, ~2017).

I believe it’s a vintage product.

It was classified as vintage since 2015 and as obsolete since 2017. Obtaining service for your Apple product after an expired warranty - Apple Support