I have some news for you all about Super Mario Bros. X's official site known as the "supermariobrosx.org" (further mentioned as "SMBX website").
Did you find that a few weeks ago, the official site of the SMBX suddenly removed its content? And the 404-not-found error appeared, and the forums only kept a work.
So, what actually happened:
(All information was taken from Shadow Yoshi, the founder of the SMBX website and its first administrator)
Maintainers of the SMBX website server received multiple DMCA takedown requests for the homepage of the site. And then, Nintendo entered into UDRP domain arbitration with Namecheap (the registrar where "supermariobrosx.org" domain was). As the "Super Mario Bros." (contained in the domain name) is Nintendo's trade mark, SMBX website maintainers figured that there was a slim to no chance of winning an arbitration. So, the whole site had migrated to a new domain, and a substantial amount of Nintendo's Intellectual Property has deleted from the site. Also, the game download link (that leads to the original SMBX game download) has been removed. So, the site's design became flatter to look different.
Nintendo took issue with how SMBX website maintainers presented the SMBX: in Nintendo's eyes, it looked like SMBX website maintainers were confusing users and making them think the game was a real Nintendo game, which they weren't, but they had a pretty good case.
Also, the SMBX website no longer contains direct download links to the SMBX game packages. Instead, now it has links to the official site of the SMBX2 (https://codehaus.moe) and TheXTech's official page (https://wohlsoft.ru/projects/TheXTech/) and gives the GitHub link to the original SMBX 1.3 source code repository, but without any resources included.
So, the new domain of the SMBX website is now:
The rest of the site content and the forum remains the same as before this migration (except for the original SMBX downloads).
Good luck to you all, and have fun!

P.S. Where are SMBX downloads?
- All original Redigit's SMBX versions from 1.0 to 1.3 are always available here: https://wohlsoft.ru/docs/SMBX_Old/info.html
- The SMBX 1.3.0.1 (a cosmetically update SMBX 1.3) is always available here: https://wohlsoft.ru/docs/SMBX_1.3.0.1/
- The TheXTech (the enhanced cross-platform port of SMBX 1.3 with updates) is always available here on the official page: https://wohlsoft.ru/projects/TheXTech/
- The Moondust Project devkit and experimental engine are always available here: https://wohlsoft.ru/projects/Moondust/
- The SMBX-38A is always available on its official page: https://smbx38a.wohlsoft.ru/
- The SMBX2 is always available on its official site: https://codehaus.moe/
Related stuff for further reading:
- https://www.smbxgame.com/forums/viewtopic.php?p=396532#p396532 The announcement of the planned migration of the host that was posted on the 5th of February, 2023.