I was recently told that some people hold that showering on Yom Tov (Hot Shower) is permitted. Where/Who does the halachah come from and what is the explanation for it? Do many people hold by this opinion? What’s your opinion on it? Thank You.

See Shulchan Aruch Orach Chayyim 511,2. The Shulchan Aruch permits washing the entire body on Yom Tov using water that was already hot before Yom Tov and therefore those Sephardim who follow the psakim of the Shulchan Aruch are allowed to shower in hot water that was heated before the chag. The Ashkenazi custom as cited by the R'ma forbids this and this remains the general Ashkenazi practice although it is questionable if the reasons behind the prohibition are still relevant (see Shmirat Shabbat Kehilchata I ch. 14 n.21).