Is it permissible to take what was deducted from the salary as a government loan, with the intention of leaving, due to the non-compliance with the agreed-upon salary?

It is not permissible to take from the debtor's money secretly, for it involves devouring wealth unjustly and betraying a trust. The proper course of action is to demand the right or refer the matter to the judiciary, as Allah Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]," and as the Prophet (peace be upon him) said: "Return the trust to the one who entrusted you, and do not betray the one who betrayed you."

As for "ظفر بالحق" (gaining one's right by force or stealth), this applies when the right is undeniably established and there is no other way to obtain it except through this method. Sheikh al-Islam Ibn Taymiyyah and his student Ibn al-Qayyim differentiated between a situation where the reason for the right is manifest, in which case the one who takes it is not considered a betrayer, and a situation where it is hidden, in which case he is considered a betrayer.