The Investopedia article that you referenced doesn't say that Form 709 is not required. It says:
"they could write one check from a joint account for the total amount and still use the gift-splitting option."
"Couples must file Form 709 if they decide to use the gift-splitting option"
"If you're a married couple and decide to split the gift, make sure you file Form 709"
Writing a check from a joint account does not automatically mean you are using gift splitting. You have to file Form 709 in order to split the gift. If the check from the joint account exceeds the annual gift tax exclusion for one person, Form 709 is required.
The annual gift tax exclusion for 2024 is $18,000. For 2025 it is $19,000.
