What is the ruling on celebrating international days, and are they considered Bidʻah (innovation), knowing that Bidʻah only applies to acts of worship? And does the ruling differ if the purpose of these days is to spread useful information and not to celebrate?

As for days designated for purely worldly occasions that have no connection to religion, are not intended as a means of drawing closer to God, and contain no elements of the pre-Islamic practices of Jahiliyyah; the ruling on observing them is based on the benefits or harms that result from them, such as Chemistry Week, Traffic Week, or Patient Care Week. There is no objection to this, as it falls under customary innovations (bid'ah 'adiyyah) rather than religious ones (bid'ah shar'iyyah).