I want to disabled Drupal 7 builtin "poormanscron" to then put it into a crontab task as it should, but when using Ultimate cron module i do not see an option to disabled Drupal 7 builtin "poormanscron"
Do i have to uninstall ultimate cron?
You don't need to uninstall any module. The setting you are looking for is on admin/config/system/cron/settings/poorman.
Change Launcher to -- Disabled -- from the default Serial, and Poormanscron should not run anymore.
If you disable or uninstall the Ultimate cron module, Drupal shows the equivalent settings in admin/config/system/cron, at the bottom of the page.
In this case, change Run cron every to Never.