Macbook air login screen shows ‘update needed’ but cannot login

Hi all,

so when i turn on my macbook air the login screen appears with two logins, the guest login and my login, but with my login it appears as ‘update needed’ instead of my username and the icon has a silhouette. I can get as far as typing in my password and then it has the apple icon and loading bar and as soon as it loads the screen just goes black. The cursor still appears but is glitchy and when you press any buttons it makes noise. I can still login to the guest login. I have restarted my laptop now countless amounts of time, and even left it for days on end hoping if i just left it it might fix itself. I'm not sure how I’m supposed to update it though if i can’t even login to update it? Very confused, please help

Would really appreciate any tips or advice, thanks