Is Not Voting in the Elections Sinful?

As explained in my previous answer, which you have referred to, that voting for a candidate standing in the elections of non-Muslim democratic countries, with the intention of improving as much as possible the circumstances that one lives in or the circumstances of other Muslims, or with the intention of preventing/minimizing harm, firmly believing that sovereignty and true hukm belongs to Allah alone, is something that is permissible, and not unlawful (haram), disbelief (kufr) or polytheism (shirk).

This is my position on the matter, and the position of the vast majority of contemporary Muslim scholars. There are many evidences for this which have been discussed in various articles and public forums, and as such, you may refer to them for more elucidation.

However, it is incorrect to make a blanket statement that voting is obligatory (fard). In the previous answer, I stated, in light of the Hadith of Sayyiduna Abu Bakr (Allah be pleased with him), that, ‘At times voting becomes necessary’ and ‘ If one is able to prevent or minimize oppression by casting a vote, then not voting would be sinful.’

Thus, the sin is only in the situation where one genuinely believes that by voting, one will be able to prevent/minimize open transgression and oppression, yet does not do so out of neglect and not having any concern for the interests of Muslims. If one abstains, however, because he feels that his vote won’t make a difference, or one does not see any benefit in voting, then there is nothing wrong with that.

And Allah knows Best