Mathematics is one of the most ignored topics in Competitive Programming.
I have seen many folks being very weak in this topic.
Try CSES maths problems set to test and improve your maths skills.
It covers some of the common fundamental techniques.
Starting 15 problems is very good for beginners, most common topics like prime sieve, divisor counting, and basic probability are covered in those problems.
Perhaps the second half may feel a bit too difficult for the not-so-experienced folks. You can take call to skip/hold those for now depending upon your skill level.
Also sharing my solutions for the same, find the link to all my solutions in the reply.