Hey, I found the solution in the meantime.
I needed to specify all these properties, and not only the two referencing my user:
FLOWABLE_IDM_APP_ADMIN_USER_ID=svgbf01
FLOWABLE_IDM_APP_ADMIN_PASSWORD=pass
FLOWABLE_IDM_APP_ADMIN_FIRST_NAME=name
FLOWABLE_IDM_APP_ADMIN_LAST_NAME=surname
FLOWABLE_IDM_APP_ADMIN_EMAIL=mail@company.hr
FLOWABLE_COMMON_APP_IDM_ADMIN_USER=svgbf01
FLOWABLE_COMMON_APP_IDM_ADMIN_PASSWORD=pass
All applications are now normally accessible.