Refresh theme
Increase the chances of successful solutions:
https://community.shopify.com/c/shopify-design/help-us-help-you/td-p/668159
Always try to fix the problem at that source:
Go into the admins navigation menus and edit the title of that menu link to be capitalized in the first place.
If that is not doable for some reason then to style capitalization with CSS:
https://stackoverflow.com/questions/5577364/make-the-first-character-uppercase-in-css
Roughly for the demo Refresh theme
https://theme-refresh-demo.myshopify.com/
Add the following css to the bottom of the themes base.css
ALWAYS back up themes before changing code.
header .list-menu__item span {
text-transform: capitalize
}
Hello @Finn4 
The easiest way is to go to Shopify Admin > Online store > Navigation and change the menu label directly, no code needed!
Hi,
Please share your store URL and if your store is password protected then also provide password too.
Thank you.
Hello @Finn4
Please could you share your store URL so that I can review it?