Show screenshot of the site for very old browsers (such as mosaic, netscape navigator, internet explorer)
To support very old browsers, render the site in a few lines of text and a screenshot. Perhaps on a legacy domain without SSL/TLS (of via google legacy mobile pages).
We got some complaints that the site does not work in IE8 in 2019. Not everybody is as fortunate to use a new generation browser of course. Also some rich organizations help themselves by mandating an abacus or a potato for surfing the web.