In the shinyapps.io dashboard only 3 months of metrics are available. Using the rsconnect API you should be able to access up to 120 days. Here is an example using rsconnect:
rsconnect::accountUsage('my-account', from = '120d', interval = '30d')
Please note that retrieving more than 3 months of data is not officially supported at this time so this functionality may be removed in the future.