Only projects working with fiscal sponsors can offer tax deductible pledges. Pledges placed to campaigns not working with a fiscal sponsor are not tax deductible.
If this is the case, the campaign page for the project will indicate that they are working with a fiscal sponsor. If you have any questions about a specific project that you want to pledge towards, we recommend messaging the creator directly and asking them about their ability to offer a tax deductible pledge.
Regarding any matters around taxes, we recommend consulting a tax professional.