All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Our answer to your questions will be summarized in the following points:
Firstly, the issue of taxes: not all taxes are forbidden; rather they should be detailed as follows:
Some of it is permissible, which is what is taken with a right cause, for the benefit of the people, such as when the state's public resources do not meet the needs of the nation and the taxes are taken to meet those needs, and to fulfill those benefits and spend for this reason.
Some of it is Islamically forbidden, which is what is taken unjustly or spent in falsehood (and inappropriately).
Secondly, the issue of the employees taking their salary from the state, when part of the resources of the state is taken from the taxes whether legitimate taxes or illegitimate taxes: there is no harm in this.
Thirdly, the issue of the work that you mentioned in the question: if you are not involved in doing what is forbidden or helping in it, then there is no harm in it in principle, nor in the salary that you get from this job, whether or not this salary is from the taxes.
For more benefit, please refer to Fataawa 203644 and 85356.
Allah knows best.