Some sites now blocked

For about a month now, some sites I used to be able to connect to are returning an error, "This site can't be reached," with ERR_CONNECTION_RESET. The site I care most about is a blog called Mike the Mad Biologist. I always use a bookmarked link to connect to it, but there are other sites, usually from links at other blogs, that get the same result. I usually use Chrome on Windows 7, so I tried Firefox and get the same result, but the other day I was using my Ubuntu 20.04 Linux setup, which uses Firefox, and was able to connect to connect to mikethemadbiologist.com without trouble. This is really annoying. I was thinking there must be a glitch at one of the DNS nodes between Thailand and Kansas, but I don't think DNS looks at what operating system sent the name resolution request. I sure would appreciate suggestions for more things to investigate.

Hello Procopius.

I can open https://mikethemadbiologist.com/

Without any issues:

I'm using Windows 10 with Firefox.

Well, yes, and I can open it with Firefox on Linux, as I said. It's when I'm using Windows 7 that this happens. I know MS support for Windows 7 ended a year and a half ago, and I know eventually Windows 7 is going to be unusable (the U.S. Navy is still using Windows XP on some of its installations). I'm mostly trying to figure out what the mechanism is that's causing this. I'm not sure, for example, whether the packet header includes operating system ID. I know when I send an HTTP request to a web site my browser is identified in some header, but it's not in the HTTP header and I don't know where to look for the structure of the request packet. I used to be able to find a lot of this stuff at Riley, but they've changed beyond recognition. I'm hoping people will furnish me with suggestions of things to research and learn about. Installing Windows 10 is not an option.

Sorry I don't know what's causing the issues your stating.
I can however give you the link to update 7 to 10 for free.

https://answers.microsoft.com/en-us/windows/forum/all/how-you-can-still-get-windows-10-for-free/2159c2a7-a925-4fa3-9a03-08a5e1ecf891

Thank you. I appreciate your generosity, and I find it interesting they're still making this offer. I installed Windows 10 when it first came out and don't like it. Later, I learned other reasons for not liking it, but initially it was just appearance. Later, I learned that two games I have on DVD cannot be installed on Windows 10 and Steam does not carry the versions I want. I suspect this internet problem has something to do with Windows 7, but I've known for years that it's eventually going to be unusable and plan to move to Linux (probably Ubuntu, but not committed). I can't run my games on Linux, either, but I'm not going to further support Microsoft.