Is it true that marriage is not obligatory and individuals who choose not to marry but remain chaste and focus on their careers will not be considered sinful?
Bismihi ta'āla
It is makruh to choose to stay single. There are numerous narrations that censure being single, and explain the many benefits of marriage.
The only time marriage would be obligatory is if one falls into sin, and marriage would solve that problem.
One can combine between marriage and focus on career as well.
And Allah knows best