Is it advisable to for someone who is just starting his preparation for CSE 2023, to take maths optional?

Maths is a double edged sword. Only pro of taking maths optional is that one or two people ever year able to breach 320/330 mark, so you could be one of them. Rest everything is a con. I have written two Mains with Maths optional and have decent background and hold over the subject but 300 plus is still a dream for me. See having interest and background is necessary but no where sufficient. I know few people who qualified the exam after switching to humanities from Maths. Maths is rewarding for few but very risky for others. You will not get enough time for GS so will loose marks there. If you can compensate that by scoring extraordinary in Maths, it could be taken otherwise see other options.