modartt.com is unreachable for days

Both modartt and the forums are working for me.  If you're comfortable with cli/command-line, you could run a traceroute/tracert request, ICMP ping command, or DNS dig command and see if the IP is unreachable or the DNS is incorrectly cached or something like that.  You could also open the Network Inspection tool (in a browser like Firefox or Chrome) and see if there's anything logged about response headers, delay timeouts, etc. (e.g. if the server/service is reachable but timing out specifically for your connections and requests).  You can flush your dns cache on Windows or Linux--a small, temporary performance hit but nothing big at all.  If you're behind a VPN or proxy, that could be interfering with the connection--or on the other hand, a VPN might allow you to route around something that is otherwise blocking your connection upstream.  The fact that it's been days and days makes a caching problem less likely but not impossible.

There are also tons of ways that myriad malicious and non-malicious actors sever, change, update, reroute, modify, or repair connections all the time that go in-between connections many times a day across the entire "web."  (E.g. road crews can accidentally cut a fiber connection that drops or degrades internet for an entire region or country--especially in less industrialized areas where redundancy and failovers aren't as readily present or practical, and hackers can mess up just about anything that--like a power grid--will impact only a subset of the "internet" at large...)  While it's tremendously difficult to bring down the entire internet, even that can and has been done before (thankfully accidentally) like when--if memory serves--a root certificate for TLD (top-level domains--basically the whole internet) was mishandled and read as expired and the expiration was cached downstream, which broke DNS for most of the planet for many hours.

Without knowing details about your computer, internet browser, network connection, ISP, region/country, etc., the most beyond the above that I can suggest is the best wishes that whatever's wrong clears up as quickly as possible for you!  Keep us posted, if you can.