It seems bug which comes form update. You may raise it to Microsoft. Hope Microsoft will fix it soon.
Please contact your admin/IT department create a support ticket via Microsoft 365 Admin Center> Support> New service request. Support team there will have the correct channel and resources to help you investigate more and find what exactly the reason has caused this situation.
Get support - Microsoft 365 admin | Microsoft Learn
Similar issue here.
Scroll Thumb locks in Data Validation Drop Down List - Microsoft Community