68 for mobile is not a great score. the link you refer to it’s probably not made in bubble but with ghost (there is this tag <meta name="generator" content="Ghost 5.80">). there are a lot of topics about speed score of bubble apps in this forum, mainly what you can do is to keep your page small and load only the minimum data needed.
read the page source: a meta tag that says ghost is the generator, no standard bubble js or css loaded. a lot of good signs about not being built with bubble