Is there a site to play Go online against a computer, in 2018?
The accepted answer in your linked question is still valid: ELF (the Facebook go bot, account name "ELF") or variants of LeelaZero play on the Kiseido Go Server (usually bots have "LeelaZero" or "LZ" in their names). You can find a list of these bots in the room "Computer Go" (Menu "Rooms" > Room List > Social > Computer Go)