When your browser connects to a website, it will tell the webserver what type of browser you are using in the HTTP headers. This can be used for serving a special web page for browsers with quirks, or it can be used to block certain browsers.

It may look something like this:

User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:123.0) Gecko/20100101 Firefox/123.0

But you can use an extension like this one to spoof your user agent and send out one that corresponds to a chromium browser.