Can someone explain the phrase "Certainty is not removed by doubt."

Asallam alaikom ww,

I am F revert 42.

I am recivering from a health problem which necessitates praying whilst seated in a chair.

Recently, I have been experiencing frequent waswas regarding the possibility that I may be missing certain pillars, such as rising fully after rukūʿ—including the recitation of ‘Samiʿa Allahu liman ḥamidah, Rabbana wa laka al-ḥamd’—before proceeding to sujood.

As a result, I would repeat the rakʿah and then perform the two prostrations at the end.

I looked online and read that if the doubts are becoming frequent, then just ignore them and the the statement : "Certainty is not removed by doubt" came up and I don't quite understand what that means.

Have I done the right thing by ignoring these doubts ? And what does the statement mean ?

Jazak'Allah kheiran for reading from me.