You closed your OR() function on itself after {End Date}. The structure of OR() is OR(this, that, etc.), whereas you have it as OR(this), (that), (etc.)). While you can technically add the parantheses for each value if you want, it’s redundant and in this case you’d need to make sure you opened “this” with a paranthesis too. You also have an extra comma at the end - you only need to place them between values. This will work:
IF( OR( TODAY() < {End Date}, {# Remaining} >= 1),
“Active”,
“Expired”
)