أحسن الله إليكم، I wrote down many du’a’s (both sunnah and my own) and read from them/say them daily. Would this daily practice be considered a bidah? جزاكم الله خيرًا

No, it is not a bidah, and you may supplicate with whatever good supplications you love. Only diversify and do not keep to the same ones every time, and give the duas of the Prophet ﷺ priority.