So I literally see this everywhere and have no idea what this means but by guess is that they’re word because I see it in shiritori and kinda like haunts me.
N5 → N1 refers to the five levels of the JLPT (Japanese-Language Proficiency Test). N5 is the lowest; N1 is the highest. When you see a word, kanji, or grammar labeled with an N-level, that's just an educated guess as to which test you're likely to need it for.
"Help and Support" has this:
" If given, the JLPT level is an educated guess by the renshuu staff as to which level this grammar belongs to on the JLPT (Japanese Language Proficiency Test). Unfortunately, there are no longer any official grammar lists for the JLPT. "
It says "grammar", but it should also apply for the other two. AFAIK, there are no official lists.