elsslots

No, it's true that that in particular is not a para-site, but just by doing a research you will find too many!

About the most official site ever of the Cenacolo, I don't get exactly if they have tweaked something recently, but the most functional site (in Italian and English) is

https://cenacolovinciano.org/en/

The one of the Ministry is indeed official, but still just links to this site, and, most importantly, for some arcane reason its English version lacks this link (but has an email adress). I hope this site will remain stable for now. There are still some loops to go through to reach the ticketing site (Visit -> How to book -> licensee link). For some reason, at the moment, availability seems to consider the current week only.

Official websites and related websites of the 2021 inscriptions:

Amami-Oshima Island etc. – two more National Parks with inscribed areas on Okinawa and Irimote
https://www.env.go.jp/en/nature/nps/park/yambaru/index.html
http://www.env.go.jp/en/nature/nps/park/iriomote/index.html

Arslantepe, including a nice youtube video showing what you can expect
https://turkishmuseums.com/museum/detail/2142-malatya-arslantepe-archaeological-site-and-open-air-museum/2142/4

As-Salt
https://international.visitjordan.com/Wheretogo/AsSalt.aspx

Danube Limes, website of the Roman City of Carnuntum
https://www.carnuntum.at/en?set_language=en

Jomon, nomination website with information on the serial sites (access, opening times, admission fees, links to websites etc)
https://jomon-japan.jp/en/

Ljubljana
https://www.visitljubljana.com/en/visitors/explore/things-to-do/sightseeing/article/plecniks-ljubljana/

Nice
https://en.nicetourisme.com/

Padova, nomination website, not up-to-date but with detailed descriptions
https://www.padovaurbspicta.org/padova-urb-picta-english/

Madrid, El Retiro on the Madrid Tourism Website
https://www.esmadrid.com/en/tourist-information/parque-del-retiro?utm_referrer=https%3A//www.spain.info/

Porticoes of Bologna, Tourism website and the Santuario San Luca
https://www.bolognawelcome.com/en/blog/the-porticoes-of-bologna
https://www.santuariodisanluca.it/eng/

Thanks, Hubert! I have added them, they will show when the site is refreshed during the coming day.

The two links for Tusi sites are both invalid and on quick glance there isn't an official website :(

Thanks for checking! I've removed them