What’s on my betta’s head

Hey guys, this is Marvin. He is my alien betta and this is his third day with me. He lives in a 36L planted tank with 6 Pygmy corys and 10 Sakura shrimps they are totally ok with each other. I have a hob filter and the temp is 26°C. Water parameters are all looking good (0 NO3, 0 NO2, pH 6,5) I have botanicals in the tank. I fed him with three different types of food (Omega One Betta Pellets, Sera Bettagran, Tetra Larva Sticks) and he ate each one.

Today I noticed something is weird on his head. And I need help with that. Am I overreacting? This thing wasn’t there yesterday and I checked the photos I took.