I tamed a squid lvl 150 on the 28th of April 2022. You need a mount with a lot of heath and a good saddle, or be ready to sacrifice. I used and suggest shadowmanes. When you find a squid let him grab your mount, then dismount (you can also dismount before, not important) and then reach his mouth to feed him 50 BP. Your mount will be grabbed for some decades of seconds and a non mate boosted shadowmane (80 natural armor) takes around 2000/3000 DMG by a single Tuso with 215% DMG. If there are other aggressive dinos near the Tuso, they will aggro your shadowmane so you have two choices: A) you get a lot of damage while grabbed, like 6/7k hp lost, otherwise B) you kill everything near squid. But since squid swims around, I suggest to be helped by somebody ho kites around sharks, eels and so on. After every feed the food needs to go down by 1500 points, which is quite slow (takes around 10 minutes). So be ready to wait somewhere. With shadomane I suggest to cloack and stand where you want. Then repeat until it's tamed. I didn't render it for some time, while still being not too far and the taming didn't interrupt. Taming efficiency and taming percentage do not go down if squid takes damage or waits too much time.

Bye bye! Remember, it's dangerous underwater, always!