If you look at Optimum’s support page, you’ll get a list of supported modems. Almost none of those are actually available for sale.
On the bottom, they tell you to go to the website http://www.arrismodemsitecsc.com/ to buy a modem. This redirects you to http://shop.surfboard.com/optimum-store/ which now shows nothing, but yesterday showed two out of stock modems and one pre-order modem. These are the officially supported modems.
There are multiple websites that tell you there’s a whole bunch of approved modems, but Optimum officially supports just a few models, mainly from Arris. Others may work, it might not. I specifically looked for a comment or review that said “I bought this modem and it works with Optimum.