In the Official Microsoft Flight Simulator > Wishlist and Bug Reporting Hub categories, there are votes possible for users. At the top of the page, near the opening post, you should be able to find a blue Vote-button. Click it and you’ve just voted for that item. Find details in the guide about it:
If you happen to open a bug report yourself or a wishlist item, make sure to vote for it as well, as there is no automation in this regard.