By using my ETH coin to purchase an NFT, have I just committed a
potentially taxable event?
Yes. When you purchase something with cryptocurrency, this is treated as a barter transaction for income tax purposes. Also, generally speaking, both an ETH coin and an NFT would be considered to be capital assets for tax purposes, just like investment securities like stocks and bonds.
When exceptions do not apply (and no exceptions are applicable here), a barter transaction is taxed as if you sold the asset you are relinquishing in the barter for U.S. dollars at a fair market value rate, and then purchased the item you obtained in the barter in cash for that amount of U.S. dollars.
If you purchased your ETH coin for fewer U.S. dollars than the ETH coin was worth when you bought the NFT, then you will have a capital gain in the transaction. If you purchased the ETH coin for more U.S. dollars than the ETH coin was worth when you bought the NFT, then you will have a capital loss in the transaction (although, because it is a capital loss, you may not be able to apply this loss to reduce you ordinary income immediately).
I do not address sales taxes in this answer. The definition of a taxable sale varies considerably from state to state and the question of whether a purchase of an NFT is a taxable sale is simply an undefined open question in many sales taxing jurisdictions. Also, it is not at all obvious under what circumstances a particular sales taxing jurisdiction would have the authority to tax a particular NFT purchase. This would be a highly fact specific inquiry.