Can i use an asset if it has no license but its free to use?

so i found a PSD file of a phone mockup, but in the description of the item they said “You can use it!” , however it’s not under any license, can i use it in my theme? , i also can’t contact them for a license since their company is Discontinued, i really want to use the mockup but i’m not sure, i don’t want my theme to get rejected for this.

I’d say no. You need to own or have the right to use, everything included in your item. The “You can use it!” licensing terms aren’t comprehensive enough to know for certain whether it’s ok to use the item commercially, include it in stock or redistribute it… so you can’t say for certain that you have the right to use it in your item. Best to be on the safe side and not use it.