Unbox T with Unsafe.Unbox<T>(val) will remove allocation. https://twitter.com/badamczewski01/status/1452918677855145988

DotnetUwrapOptimization.cs

BenchmarkRunner.Run<BenchmarkUnbox>();

[BenchmarkDotNet.Attributes.MemoryDiagnoser]
public class BenchmarkUnbox
{
    [Benchmark]
    public void Slow()
    {
        A(0);
    }

    [Benchmark]
    public void Fast()
    {
        B(0);
    }

    void A(int x)
    {
        object o = x;
        for (var i = 0; i < 1000; i++)
            Inc((int)o);
    }
    object Inc(int x) => ++x;

    void B(int x)
    {
        object o = x;
        for (var i = 0; i < 1000; i++)
            Unsafe.Unbox<int>(o)++;
    }
}

Result_BenchmarkRunner_NET5.txt

// Validating benchmarks:
Assembly LINQPadQuery, Version=1.0.0.336, Culture=neutral, PublicKeyToken=null is located in temp. If you are running benchmarks from xUnit you need to disable shadow copy. It's not supported by design.
// ***** BenchmarkRunner: Start   *****

// * Summary *

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
AMD Ryzen 9 5900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK=6.0.100-rc.2.21505.57
  [Host] : .NET 5.0.11 (5.0.1121.47308), X64 RyuJIT


| Method |       Mean |    Error |   StdDev |  Gen 0 | Allocated |
|------- |-----------:|---------:|---------:|-------:|----------:|
|   Slow | 3,261.2 ns | 14.15 ns | 13.23 ns | 1.4343 |  24,024 B |
|   Fast |   219.2 ns |  0.36 ns |  0.32 ns | 0.0014 |      24 B |

// * Legends *
  Mean      : Arithmetic mean of all measurements
  Error     : Half of 99.9% confidence interval
  StdDev    : Standard deviation of all measurements
  Gen 0     : GC Generation 0 collects per 1000 operations
  Allocated : Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
  1 ns      : 1 Nanosecond (0.000000001 sec)

// * Diagnostic Output - MemoryDiagnoser *


// ***** BenchmarkRunner: End *****
// ** Remained 0 benchmark(s) to run **
Run time: 00:00:46 (46.71 sec), executed benchmarks: 2

Global total time: 00:00:46 (46.71 sec), executed benchmarks: 2
// * Artifacts cleanup *

Result_BenchmarkRunner_NET6.txt

// Validating benchmarks:
Assembly LINQPadQuery, Version=1.0.0.4, Culture=neutral, PublicKeyToken=null is located in temp. If you are running benchmarks from xUnit you need to disable shadow copy. It's not supported by design.
// ***** BenchmarkRunner: Start   *****

// * Summary *

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
AMD Ryzen 9 5900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK=6.0.100-rc.2.21505.57
  [Host] : .NET 6.0.0 (6.0.21.48005), X64 RyuJIT


| Method |       Mean |    Error |   StdDev |  Gen 0 | Allocated |
|------- |-----------:|---------:|---------:|-------:|----------:|
|   Slow | 3,501.2 ns | 58.68 ns | 54.89 ns | 1.4343 |  24,024 B |
|   Fast |   219.6 ns |  1.14 ns |  1.01 ns | 0.0014 |      24 B |

// * Legends *
  Mean      : Arithmetic mean of all measurements
  Error     : Half of 99.9% confidence interval
  StdDev    : Standard deviation of all measurements
  Gen 0     : GC Generation 0 collects per 1000 operations
  Allocated : Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
  1 ns      : 1 Nanosecond (0.000000001 sec)

// * Diagnostic Output - MemoryDiagnoser *


// ***** BenchmarkRunner: End *****
// ** Remained 0 benchmark(s) to run **
Run time: 00:00:48 (48.68 sec), executed benchmarks: 2

Global total time: 00:00:48 (48.72 sec), executed benchmarks: 2
// * Artifacts cleanup *