most picrews and meiker's will specify whats allowed between personal or commercial use but if you're uncertain it's best to double check their info panels and gauge based on that
for example picrew overall has this pop-up to show differences in use

and links to a more detailed explanation here: https://support.picrew.me/en/about_picrew_player/promise
The biggest difference is usually "are you making money with this" or not but some get more specific with their rules.
If you're really hard pressed you can always see if an artists is willing to offer icon or cover artwork at free or reduced prices but don't be mad if someone says no. You could also try to make your own visual assets using stock photos or free to use clip art just be mindful of whether or not something is ai generated as it's against Tapas TOS.
A big big thing if you do use a picrew or meiker for your cover art is to provide credit to where you got the art which usually will be the link to the picrew/meiker itself or the artist who made it, which most have a handle for their sns in the description or attached to the maker itself
All said best of luck getting a cover together 