You’re confusing a means with an act of worship.
Nobody believes that Friday reminders themselves are Sunnah or rewarded independently. The Sunnah is increasing salawat on Friday, and reminding people of an established Sunnah falls under the general command to remind the believers.
Otherwise, weekly classes, Ramadan reminders, prayer timetables, and reminders to read Surah al-Kahf on Fridays would all become bid’ah simply because they happen regularly.
The issue isn’t regularity. The issue is introducing a new act of worship into the religion.
So where is the evidence that reminding people of a legislated Sunnah on the very day that Sunnah is prescribed is an innovation?
Be grateful to your mother everyday and never leave her out of your duas. Don’t fall for the shaytan trap imitating the disbelievers to thank your mother once a year.
The Prophet ﷺ said, whoever goes to bed in a state of wudu, then wakes up at night and asks Allah for something in this world or the hereafter, it will be given to him.
[Sunan ibn Majah, 3881]