Реализация валидации в Blazor не по потере фокуса, а по нажатию кнопок: https://www.meziantou.net/validating-an-input-on-keypress-instead-of-on-change-in-blazor.htm
Meziantou's blog
Validating an input on keypress instead of on change in Blazor - Gérald Barré
In this post, I describe how to validate an input element on the oninput event instead of the onchanged event in ASP.NET Core Blazor.