Unity C# FPS Counter - Add to any GameObject, then assign any Text using inspector.

FPSCounter.cs

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class FPSCounter : MonoBehaviour
{
	public enum DeltaTimeType
	{
		Smooth,
		Unscaled
	}

	public Text Text;
	[Tooltip("Unscaled is more accurate, but jumpy, or if your game modifies Time.timeScale. Use Smooth for smoothDeltaTime.")]
	public DeltaTimeType DeltaType = DeltaTimeType.Smooth;

	private Dictionary<int, string> CachedNumberStrings = new();

	private int[] _frameRateSamples;
	private int _cacheNumbersAmount = 300;
	private int _averageFromAmount = 30;
	private int _averageCounter;
	private int _currentAveraged;

	void Awake()
	{
		// Cache strings and create array
		{
			for (int i = 0; i < _cacheNumbersAmount; i++) {
				CachedNumberStrings[i] = i.ToString();
			}

			_frameRateSamples = new int[_averageFromAmount];
		}
	}

	void Update()
	{
		// Sample
		{
			var currentFrame = (int)Math.Round(1f / DeltaType switch
			{
				DeltaTimeType.Smooth => Time.smoothDeltaTime,
				DeltaTimeType.Unscaled => Time.unscaledDeltaTime,
				_ => Time.unscaledDeltaTime
			});
			_frameRateSamples[_averageCounter] = currentFrame;
		}

		// Average
		{
			var average = 0f;

			foreach (var frameRate in _frameRateSamples) {
				average += frameRate;
			}

			_currentAveraged = (int)Math.Round(average / _averageFromAmount);
			_averageCounter = (_averageCounter + 1) % _averageFromAmount;
		}

		// Assign to UI
		{
			Text.text = _currentAveraged switch
			{
				var x when x >= 0 && x < _cacheNumbersAmount => CachedNumberStrings[x],
				var x when x >= _cacheNumbersAmount => $"> {_cacheNumbersAmount}",
				var x when x < 0 => "< 0",
				_ => "?"
			};
		}
	}
}