I have made this blog to add links and information of all oi contest(official contest/mirror) happening this year.I missed out IZHO and infocup(didn't come to know and no blog post on cf as well).Please post a comment if you know any other OI contest with contest date/registeration date or link
JOI final round- https://contests.ioi-jp.org/joi-ho-2021/index-en.html
toki cms contest- https://codeforces.me/blog/entry/85545
Finnish Olympiad in Informatics- https://codeforces.me/blog/entry/87261
infocup- https://www.info1cup.com/#schedule
COCI- https://hsin.hr/coci/
usaco- http://www.usaco.org/
APIO 2021- https://apio2021.id/
IOI 2021- https://ioi2021.sg/