Hi, @Serdar2023 !
Thanks for getting back to me. I understand the issue and I apologize if you thought my answer was generic.
The reason you’re not able to select Ontario as an option is likely because you already added Ontario/Canada as a region to collect taxes. When doing so, the only further options that appear are the provinces with separate PST rates (BC, Manitoba, Québec, and Saskatchewan).
To rectify this and ensure you’re collecting the correct taxes, you can delete the existing tax rate, and then add Ontario, as shown in these screenshots:
Once you’ve added the region, sales tax is automatically calculated and applied to orders.
Let me know if you have any other questions or need further assistance with this!