Is complete certainty required that semen has not exited, or is the preponderance of suspicion sufficient for the non-necessity of ghusl in the event of feeling the movement of semen without intercourse and restraining it? And is ghusl required if the exit of semen is not verified after restraining it, or if I see a small drop closer to madhy (pre-seminal fluid) and cannot definitively confirm it to be madhy?

"Whoever feels the movement of semen with desire, then holds his penis and nothing comes out, is not required to perform ghusl according to the majority of scholars. The default is that semen has not exited until it is certain that it has. If it is certain that it has exited, then ghusl is obligatory. But if you are not certain of its exit, then ghusl is not incumbent upon you. As for the drop you saw and doubted, you have the choice to consider it either semen or madhiy (pre-seminal fluid)."