Hello. There are a number of free tools on the web such as : Google insight Gt metrix Pingdom tools Let's say the guys at the link https://barwenock.com/services-details/magento-upgrade.html helped me with magento performance audit. If you have an extra couple of dollars, I advise you to contact them. Good sales!
GTMetrix performance, we were getting Grade A 95% on category pages and Grade A 97% on product pages, Magento 2.x is very resource heavy especially if you use 2.4 with Elasticsearch, you need Redis, opcache, 2.x is not friendly to lower end servers and there's usually very little you can do.