theHigherGeometer on Nostr: Oh, it was definitely pronounced as "th" in Old English, the writing at the time ...

Oh, it was definitely pronounced as "th" in Old English, the writing at the time using ð and þ shows that. The -s ending was a Northern dialect thing (from the Old Norse influence), and it was eventually adopted further south. Shakespeare mixed the use of -s and -eth, so matters were definitely shifting strongly by that point at the latest. I saw one person claim in a discussion that by the late 1600s the -s/-es ending had mostly won out, except for certain common words like hath and doth.