Website speed is the most important factor in Technical SEO. When user visit website and it takes time to load, user return back and this cause an effect of CTR. websites speed should be more then 1.3 sec from First paintful content and Last paintful content for better users experiences.
Faster websites give users a better experience, which means they stay longer and interact more.
Google uses page speed as a factor in ranking, so it's important for SEO.
Since more people are using mobile devices to visit websites, mobile optimization is a must.
A mobile-friendly site changes to fit different screen sizes, making it easier to use.