ReadOnlyMemoryConverter.cs

await using var context = new BlogContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void ConfigureConventions(ModelConfigurationBuilder configurationBuilder)
        => configurationBuilder.Properties<ReadOnlyMemory<byte>>().HaveConversion<ReadOnlyMemoryConverter>();

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer("Server=localhost;Database=test;User=SA;Password=Abcd5678;Connect Timeout=60;ConnectRetryCount=0;Encrypt=false")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    private class ReadOnlyMemoryConverter() : ValueConverter<ReadOnlyMemory<byte>, byte[]>(v => v.ToArray(), v => v);
}

public class Blog
{
    public int Id { get; set; }
    public ReadOnlyMemory<byte> Bytes { get; set; }
}

Is it on by default? Or do I have to do something?

It's enabled by default - have you seen some other behavior?

Does it allow queries comparing dates?

No, because comparing the string representations of DateTimeOffset doesn't work - imagine having different time zones there, and then comparing string representations. If you're only storing timestamps in a single timezone (e.g. UTC), you can just use DateTime, which has a default value where comparison is supported.