Hello Wayeyade
You probably mean the Swiss Travel Pass.
Yes, the Swiss Travel Pass is valid on the mentioned route (Bus no. 50 to Basel SBB, IC 61 Basel SBB to Interlaken Ost). Generally speaking, the Swiss Travel Pass is valid on all public transport providing services to inhabited places. For further information on what routes the STP is valid, kindly see the Swiss Travel Pass validity map: Swiss Travel Pass – the All-in-one-Ticket for Switzerland | SBB → Box More on the topic. → Link Map of validity
Best regards,
Roland