Hi! I am looking for theme or a bundle of themes for a jewelry designer with introduction, portfolio and blog functionality.
I hope you can recommend some themes that are well optimized (fewer requests, high lighthouse score or equivalent), recently updated or somewhat actively maintained and mobile first.
Thanks! 
The Navigator theme by Themesfisher comes to mind as it has most features you ask:
But there are also other themes. So I suggest that you go through the list over here: https://themes.gohugo.io/ and if a theme catches your eye download it and check it out locally.
Also note that there is some work-in-progress on the Hugo themes website, so some demos or parts of them may not work as expected at the moment.