Hello, i would like to see some of your sites, mainly the ones that have been upgraded to joomla 5, i want to know what you are using to help speed up your site

Examples....use latest php and optimise config Joomla with some std server cache with extensions, example NGIX proxy/Litespeed, xtra Joomla good server cache example: https://extensions.joomla.org/extension/server-cache/ etc could help and Joomla std cache server settings. Optimise htaccess settings like "Joomla masterhtaccess" settings for speed and security if you need easier use Admin Tools Pro https://www.akeeba.com/products/admin-tools.html. 

Set your security http headers in Joomla and test your site have 100% https://storejextensions.org/extensions/jspeed.html

And as a base you need a good optimized secured server with fast access, memory and dedicated cpu as a staring point. And you can tweak the user.ini and or php.ini settings in root too.

example I have working well..

;;;;;;;;;;;;;;;;;;;
; Resource Limits ;
;;;;;;;;;;;;;;;;;;;

post_max_size = 512M
upload_max_filesize = 512M
max_execution_time = 3500
max_input_time = 280
memory_limit = 16000M
max_input_vars = 6500
session.gc_maxlifetime = 1440
session.save_path = "your path"
display_errors = Off
sort_buffer_size = 512M
expose_php = Off

This little improvements make real gain in speed and wow thats really very strange but site loads much much faster.. I added it to my Joomla 5.1.2 site and really good improvements for the speed.

Compress the thumbnails #43282

https://github.com/joomla/joomla-cms/pull/43282