In Mandarin, bao is pronounced bāo, which is the first sound, not the third, see Xinhua Dictionary. Because "煲" is a dialect word from the south, most people in the north did not recognize the word "煲" before "rice cooker" became popular. After this word became popular because of the commodity, people mispronounced it as "保 (bǎo)" without careful study, and it was widely used. This is a linguistic phenomenon formed by "not knowing how to read and write" and blindly "following the crowd".

Xinhua Dictionary, 11th edition, page 16

Internet Dictionary

煲bāo（ㄅㄠˉ）

[1]walls of a pot that is steeper and straighter: 沙～. Electric rice ~.

[2]To cook or simmer in a pot: ~ rice. ~ porridge.

------〖词性与应用〗-------

Pot? bāo

Name[1][Dialect] A pot with steeper and straighter walls. E.g.: tile pot; sand pot; copper pot; rice cooker

Motion [2] To cook or simmer in a pot. E.g.: boil rice; boil porridge