we don’t know why lighthouse speed mobile is 60point - theme load fast, gtmetrix also show nice points, so maybe something is wrong by google page speed - not see something ?
Pagespeed insights uses very different parameters for testing on different devices, The main reasons why mobile PageSpeed scores are not the same as desktop PageSpeed scores are:
1- Mobile processors are slower
2-PageSpeed Insights stimulates the cell network at a slower speed
3-Mobile devices have device-specific CSS rules
So results are shown on real time testing as per these conditions.
GT matrix uses a very different approach.
To boost your website speed on Mobile you can use a third party tool like https://websitespeedy.com/ , this will fix unused javascript issue to some extend, its will also implement lazy loading and some other optimizations to boost site speed.