My tenant's rent cheque bounced - is that still a crime?

Usually no. Since 2 January 2022 (Federal Decree-Law 14/2020), bouncing a cheque for insufficient funds is decriminalised and treated as a civil debt. It stays criminal only where there is fraud - a stop-payment order, deliberately closing the account, or sabotaging the cheque. For an ordinary bounced rent cheque you pursue civil recovery, not a police case.