#makemkv dot com is still down, sort of. It's a DNS issue and someone on Reddit has the solution for now.
On Windows, edit "C:\Windows\System32\drivers\etc\hosts" and add

172.67.195.244 www.makemkv.com
172.67.195.244 makemkv.com
172.67.195.244 forum.makemkv.com

You'll need to edit the file in elevated "administrator" mode. Easiest is to just edit in notepad++ and it will prompt to elevate when needed.

Original solution here: r/makemkv