It doesn't look like traditional sails, but large spinning rotors that interact with the wind to propel the ship forward. It's called the Magnus effect.
This link has more info on it including some of the challenging issues of actually implementing it on large commercial ships.
https://www.marineinsight.com/naval-architecture/flettner-ro...
tl;dw: sails are tall and get in the way of (un)loading cargo. Fuel costs are borne by the lessee of the boat but sail costs are capital expenditures borne by the lessor.
tbf, that one's pretty easily resolved by financiers if fuel costs of typical operational use are greater than the capital costs of the masts amortised over the expected life of the vessel and the ropes and sails amortised over the expected life of the ropes and sales. There's an established market for leasing aircraft and aero engines whose value is a function of fuel economy and how much the lessees' use devalues their life limited parts.
[*] about 45 years... ;)
The less obvious issue is simply manpower and difficulty loading intermodal containers.
I'm no sailor though. Just seems like we have more ability to finely control/automate stuff in ways that weren't available in 1949.
Now these aren’t insurmountable issues on their own, but wind as supplemental power via kites or something seems like a far more viable option.