Each state makes its own laws around sales tax, so nexus thresholds and rates can vary.
If you are using Printful’s warehouse and fulfillment service, then you will have nexus where your inventory is stored.
Using Printful for print-on-demand drop shipping only does not create nexus for the seller.
In states with marketplace facilitator laws, you do not have to manage sales tax for these sales. However, they can create economic nexus, and you will need to manage and remit sales tax through other channels.