Any suggestions for speeding up site?

A few days ago, my site was loading perfectly. Now it is loading fine on desktop but on mobile it is loading very slow.
I tested pagespeed via gtmetrix and it is showing 100% but pagespeed insights is showing 59 in the speed section on mobiles.

I have tried changing theme to generatepress also but it was still showing pagespeed 38 on mobile.
I have now switched to twenty-twenty three theme in wordpress.
But still the pagespeed is 55 to 59 on mobile.

Any suggestions on how to improve it?

 

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