Since the dawn of time (if the dawn of time was in 2011), assigning Office 365 licenses has been a pain. It has never been complicated, but it has also never been a pleasant experience.
M365 - License Optimization Center
ENow Software's Microsoft License Optimization blog built by Microsoft MVPs for IT/Sys Admins.
Nathan O'Bryan MCSM
Nathan is a five time former Microsoft MVP and he specializes in Exchange, Microsoft 365, Active Directory, and cloud identity and security.