Hmm, I got br when I dropped the header (see below). Either way, the server's behavior matches the spec, so there's something up with the client if they're seeing nonsense.
Request:
GET https://jakearchibald.com/2023/against-self-closing-tags-in-html/
Accept: text/html
Ah, you know what, IntelliJ automatically adds an Accept-Encoding header if I leave it off, I didn't realize that until just now. Curl is a better test because it doesn't try to be clever.
There's still definitely something wrong with OP's client, because the server does exactly what it's supposed to.
Request:
Response: