Is it permissible to pay for transportation expenses from school funds when visiting the Directorate, given that the school donations law does not stipulate this except in the case of bringing materials by taxi?

Funds from donations are spent according to the donors' conditions. It is not permissible to dispose of school funds except for the purpose for which they were collected, based on the words of Allah Almighty: ﴿O you who have believed, fulfill [all] contracts﴾ [Al-Ma'idah: 1], and the Hadith: "Muslims are bound by their conditions." If the school donation regulations prohibit the use of its funds except for the transport fees of materials, and do not permit paying transportation allowances for employees, then you are not entitled to take anything from it for your transportation.