I need an older version of InDesign

Honestly, what you really need is a new computer. I know it sounds harsh but 6GB is barely enough to run an operating system and I doubt very much that Adobe will accept this as a reason to give you something that old and unsupported.

In addition to what Leo.r said a lot depends on what operating system you are using. If your computer is really old (and the amount of ram that you have seems to indicate that) then it sounds like even if you could get CC 2020 or 2021 it would most likely not be compatible with your computer’s OS. A new computer seems to be your best option. Sorry.

First, there's no official way to obtain older InDesign versions. Only the current + the one preceding are available (that is 2026 + 2025, as of today).  Second, nothing will work with 6 GB RAM anyway. I mean there probably some antique versions that support 6 GB officially, but it's barely enough to keep InDesign afloat anyway. The truth is that 6 GB is not enough for anything useful today. You need to either add more RAM (if you machine allows and is worth this investment) or get a new computer. I understand that it's unlikely what you want to hear but it's the reality.