High-energy (HE; ~100 GeV to 100 PeV) and ultrahigh-energy (UHE; >~ 100 PeV) neutrinos are crucial for neutrino astrophysics, high-energy astrophysics, and multimessenger astronomy. They also offer significant opportunities to study neutrino interactions, test the Standard Model of particle physics, and explore physics beyond the Standard Model. In this talk, I will first talk about final state radiation, which impacts both HE and UHE neutrino observations (https://arxiv.org/abs/2403.07984), a QED radiative correction as large as 25% while completely overlooked by current experiments. Then, on the astrophysics side, I will talk about the search for HE neutrinos choked-jet supernova using IceCube public data (https://arxiv.org/abs/2210.03088).