Can an electric cooktop be used on Yom Tov?
On Shabbos, we are forbidden from raising/lowering a fire. Chazal said that one must cover the fire – and according to some poskim, the knobs too – in case one might forget and raise the fire over Shabbos.
On Yom Tov however we are permitted to raise a (real, not electric) fire, but we may not extinguish it or lower it, and therefore this halacha does not apply for Yom Tov. However, it is still forbidden to actually raise/lower an electric appliance.
Therefore you may use an electric appliance without worry about the knobs/buttons, just make sure not to actually use the knobs/buttons.
שו”ע אדה”ז רנג, א. תצה, ב. שו”ת חלקת יעקב ח”א סי’ נ ס”ז. שש”כ פ”א אות לג.