EF Core and Postgresql generation expression is not immutable on modified_at column

I'm learning aspnet.core

In laravel we can do $table->timestamps() to generate created_at and modified_at to be updated automatically.

After searching, I found out that we can do this in EFCore (i'm using postgresql with npgsql

            modelBuilder.Entity<User>()
                .Property(u => u.created_at)
                .HasDefaultValueSql("CURRENT_TIMESTAMP")
                .ValueGeneratedOnAdd();

            modelBuilder.Entity<User>()
                .Property(u => u.modified_at)
                .HasComputedColumnSql("CURRENT_TIMESTAMP")
                .ValueGeneratedOnUpdate();

However I'm getting error:

Failed executing DbCommand (7ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] ALTER TABLE "Users" ADD modified_at timestamp without time zone GENERATED ALWAYS AS (CURRENT_TIMESTAMP) STORED; Npgsql.PostgresException (0x80004005): 42P17: generation expression is not immutable at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<g__ReadMessageLong|0>d.MoveNext() --- End of stack trace from previous location where exception was thrown --- at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<g__ReadMessageLong|0>d.MoveNext() --- End of stack trace from previous location where exception was thrown --- at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming)

I suspect the HasComputedColumnSql has couple of problem but I can't figure out why. Can anyone help?

Thanks