Is it forbidden to issue a COVID-19 vaccination certificate to someone who fears vaccination for medical reasons, such as fear of autoimmune diseases or fear of the vaccine's effect on life, if that is necessary to enable them to enter work and avoid losing their job?

It is not permissible to give a false or forged certificate regarding vaccination. The personal interest of this individual, as implied by the question, is countered by an expected public harm. The correct approach is for this person to consult the competent authorities and specialized doctors to inquire about his health condition and whether it is suitable for vaccination. If the specialists determine that his condition prevents him from receiving the vaccine, then that would serve as an excuse for his employer.