Between 1895 and 1945 Taiwan was occupied by Japan. Mao was at one point pro Taiwan independence from Japanese rule, since back then there was a strong anti colonial workers movement. After Japan capitulated, the island was given to ROC to occupy "on behalf of allied forces" (as declared by Gen McArthur). Then followed massive repressions of all leftist opposition. The ambiguous status quo since the 90s is that Taiwan retains its self governance, but foreign policy is steered by China.

Right now there are two major political parties in Taiwan: the pro independence DPP and pro status quo KMT. The left is extremely weak and divided. Imho, an independent Taiwan only serves US foreign interests, so would be skeptical of any movement that supports it. Taiwan's presidential elections are scheduled for January 2024, it is likely that DPP will hold on to the position. Their VP candidate is a former diplomat to the US. It is very obvious that their stance for independence is a stance for cozying up with the States.

To summarize, there was a period of time when an independent Taiwan would be in leftist interests, but at the moment that is not the case.

Taiwan has been under Chinese influence since the Han dynasty 2000 years ago. After the fall of the Ming dynasty in the 1640s, a Ming prince fled to the island and set up his own rogue kingdom, which was reunified with the Qing dynasty in the 1680s. Taiwan then became a prefecture of Fujian Province until 1885, when it became its own province. Japan occupied it in 1895 and controlled it until 1945, when the Allies signed a treaty returning it to China, which was in a civil war at the time.

The left was mass murdered, as it was usual during the mid 20th century.

Doesn't even need to be a marxist take, regular history is enough