Unfortunately, many simply don't work for 99.9% of the modern Web due to it requiring TLS 1.3. For example, on Windows 98,there is a myth of some Opera version that had TLS 1.3 support, but I haven't had a chance of finding it. TLS 1.2 is the latest one can get
It is quite ironic that it is not JavaScript, or the modern dynamic Web features that prove most difficult to back port to old operating systems, but SSL.
Of course there is the Web proxy that renders modern Web as an image map accessible even to the oldest computers, but this is "cheating" as you really are using a modern OS to sort of pre-digest content. You need a modern OS constantly running to use your vintage machine just in case you might need to download some file from the Web.