That is not true at all. You need to have that initially in the bank but you can absolutely spend it on whatever the company needs - services, wages, things. You can absolutely have a GmbH or UG without any cash left.
Is the finances of a UG/GmbH public information in Germany and easily obtained by citizens?
You need to file an end of year statement (Bilanz) with the register court the year after and these can be obtained for a moderate fee. The exact details on what needs to be filed depend on the size of the company, details (in german) are in this article https://www.gmbh-guide.de/jahresabschluss-bundesanzeiger.htm...
You have to submit your balance sheet each year, and with a short lag it is available online on https://www.handelsregister.de where you can buy the info on any GmbH incl. persons who own it.