Linq should not be used on hot paths, as it causes GC pressure. If this is what bothers your program, you can find out by profiling.
However, if you have some slow SQL query or redundant SQL queries, I bet it is performance wise better to do something about that.
In the case of Roslyn, the C# compiler, they avoid Linq on the hot paths (which run many times, for instance when typing in Visual Studio!) but outside hot paths linq is still used.
Which is annoying as hell once you are used to LINQ. I completely forgot how to write a for loop till .NET Core came up with Span<T> and friendly forced us to re-think about memory.
I hope they update LINQ in .NET to address these use cases.
However, if you have some slow SQL query or redundant SQL queries, I bet it is performance wise better to do something about that.
In the case of Roslyn, the C# compiler, they avoid Linq on the hot paths (which run many times, for instance when typing in Visual Studio!) but outside hot paths linq is still used.