Recently I found how to disable suggestion list in C# and F# completely even after special characters like "." are typed. This is possible in Visual Studio 2022.

There is a checkbox in Options. Path to the checkbox: Options -> Text Editor -> All languages -> Auto list members. Uncheck this checkbox and after that completion list will not popup after "." automatically.

If you want to disable completion list to popup automatically after part of the statement already input in C#/F# you need to uncheck another checkbox in options. Path To the checkbox: Options -> Text Editor -> C# (F#) -> Show completion list after a chracter is typed.