Hi, it depends on how the freebie was offered.
E.g. if there were mentioned some licence terms.
On sites like Sketchfab, you can get free props but they are often bound to CC (Creative Commons) or similar licenses.
Each license defines what you can do with them. For example, you can use it in your own work and commercial work, but you have to attribute the creator.

If for your freebies there is stated nothing else than 'freebie', than i would suspect that is completely free.
As such you are allowed to do everything you want with it.

However, if you are unsure, it is always best to contact the site owners / content creators and ask them about that.

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