The PRC left those islands to the ROC for a reason. If China retook those territories like Kinmen and the Penghu, thus the population in them who have more traditional ties with the mainland than the island of Taiwan, the PRC would only be forcing their own hand as it'd just make it that much easier for the 'Taiwanese' to declare independence.
Where do you think Taiwan is heading towards by first inviting/accepting visit by Pelosi, and then follow with other heads of state ? May be Tsai just loves parties with foreign dignitaries.
Where do you want to draw the red line ? Obviously, China essentially declared the Pelosi visit is beyond China's red line.
Agree with you that China leaving Kinmen and Matsu alone for obvious reasons. While reclaiming them is relatively easy, they do not add much to China's strategic and military position other than antagonizing Taiwan. So taking them for no particular reason is not advisable.
But Penghu is another story. It has significant strategic value, as mentioned by quite a few SDF members. But it is far more militarily challenging to take control of, and China probably was not capable of capturing and holding it until recently.
Given the current geopolitical situation, taking Penghu and then Matsu and Kinmen (in that order) makes sense and will significantly enhance China's capability to control the Taiwan Strait and eventual force reunification.