Japan did not specify a recipient party of Taiwan’s sovereignty because it was not up to Japan to decide. It was up to US. Hence the wording was that Japan renounces the right, the title and the claim (all three) so that US can do what it wanted and when it wanted with Formosa. If you read closely, it does not relieve Japan from any responsibility and liability, even though Japan looses the right and benefits.
If you read closely, if there is no claimant to Formosa, US can still transfer right title and claim to Japan by default.
There is at least one claimant to Formosa, and that is China. However China is prohibited from being entitled to any rights and benefits due to Article 25. Therefore China does not qualify. Suppose Japan, for whatever reason, wanted to let China have Taiwan, Japan still could not do so without violating the Peace Treaty, due to the fact that Japan already renounced the power to transfer any right in Article 2. It’s not up to Japan even if Japan wanted to help China to acquire Formosa.
Furthermore, if Formosa is rendered into chaos and it’s become that Formosa now poses a threat to US (for example became a hotbed of anti-US militant/terrorists groups), Japan could still be liable for neglect. The Peace Treaty does not excuse Japan from not defending Taiwan. (Defending simply means not to allow a territory to fall into hostile hands.)