I married a foreign national in 2018 but I have not sponsored her yet as we are still overseas. Therefore my spouse does not have a SIN. Can I use Turbotax without it?

Yes. You can put your spouse's SIN as 000 000 000. Also, unless you can prove that you supported your spouse (with money transfer, etc…), then it’s best not to take the spousal amount: https://turbotax.community.intuit.ca/replies/2647950