Is it permissible for me to work in the field of writing and auditing construction contracts and letters of credit for a company that deals with usurious banks and requires bank guarantees and insurance documents, knowing that these conditions are unchangeable and I currently have no other job available?

The default rule is that it is permissible to work in writing contracts, but on condition that they conform to Sharia. If they include a Sharia violation, it is not permissible to work with them because that constitutes assistance in sin. It is not permissible to work in writing and authenticating contracts that contain forbidden conditions, such as usurious transactions or commercial insurance. If the majority of clients engage in forbidden transactions and your work necessitates authenticating and following up on them, and you cannot avoid it, then you must leave it. However, if you cannot find any other work and you are in need of it, then it is permissible for you to remain in it until you find another, while actively searching for one.