The fact that the Romulan Star Empire joined the Typhon Pact does not necessarily mean that the Treaty of Algeron is nullified. After all, the fact that the United States joined the North Atlantic Treaty Organization did not affect its obligations under the Treaty of San Francisco.
On the other hand, if the Treaty of Algeron banned the Romulan Star Empire from spreading cloaking technology, yet it has done so to its Typhon Pact partners, this
likely nullifies the Treaty -- or, at least, means that neither party should feel obligated to enforce it anymore.
On the other hand, it's entirely possible that the Treaty did not contain any provisions banning the RSE from sharing cloaking technology -- The Lost Era: Serpents Among the Ruins
establishes it to have been the treaty that ended the ever-escalating tensions between the UFP and RSE in the wake of the Khitomer Accords following the Tomed Incident, and that the Federation-won't-cloak provisions were foisted upon the UFP as part of the Treaty. In which case, the Treaty is still in force and the Federation will have to continue relying upon its legally-cloaking allies for missions requiring a cloak. The UFP will have an advantage insofar as the Imperial Romulan State adds a new cloak-capable partner to the Khitomer Accords Alliance.