I understand how hard birthdays are during this pandemic times, mine was a few weeks ago and it was odd. But don´t feel bad about people not posting on their stories wishing you happy birthday, if you think about it it´s a somewhat pointless thing and more for show than anything else.Focus on those that wished you happy birthday like that one friend you mentioned. Quantity does not equal quality.
It´s just another day of isolation if you make it seem like just another day. Try to make something that you enjoy, even if you do it alone. Or just talk to strangers online ( in a safe way) , that can sometimes help if you´re feeling lonely. And you should try to do that not only during your birthday but more often so this situation can be a bit more bearable.
Other than that Happy Birthday! Try to keep your head up, you´re only starting your twenties and things will get better.