Tangut character for disease

It refers broadly to illness, not one named condition.

Is 𗈏 a Chinese character?

No. It belongs to Tangut, a distinct language and writing system.

Western Xia ruler Li Yuanhao ordered the Tangut script in 1036 as a state-building project. It gave the Tangut language an official written form and helped distinguish Western Xia from China’s Song dynasty. Its square forms and character-building principles were inspired by Chinese writing, while Tangut remained a separate language and writing system.

Khitan rulers had created two scripts about a century earlier, one largely based on Chinese characters; Jurchen rulers later created one for their own language. These show a regional practice of designing scripts for local languages. Surviving Tangut texts include Buddhist scriptures, translations from Chinese or Tibetan, Confucian classics, military treatises, literature and official records. One manuscript from the ruins of Khara-Khoto in Inner Mongolia probably dates to the 12th or early 13th century; Tangut Buddhist texts and printing continued after Western Xia fell in 1227.