This is not new, I experienced this the last time it happened and the same incident
also occurred in 2020 . I wouldn’t be too worried about the 503 error message if I were you, try rebooting your device or using a different browser. I’m always login to the forum and everything seems to be working fine on my end.
What to do if the site BITCOINTALK.ORG is unavailable?
If BITCOINTALK.ORG works, but you cannot access the site or its individual page, try one of the possible solutions:
Browser cache.
To delete the cache and get the current version of the page, refresh the page in the browser using the key combination Ctrl + F5.
Access to the site is blocked.
Clear your browser cookies and change the IP address of the computer.
Antivirus and firewall. Check that anti-virus programs (McAfee, Kaspersky Antivirus or an analogue) or a firewall installed on your computer do not block access to BITCOINTALK.ORG.
DNS cache.
Clear the DNS cache on your computer and try to access the site again.
VPN and alternative DNS services.
VPN: for example, NordVPN;
Alternative DNS: OpenDNS or Google Public DNS.
Browser Plugins.
For example, the AdBlock extension, along with ads, can block the content of a site. Find and disable similar plugins for your site.
Source:
https://updownradar.com/status/bitcointalk.org