Since Matomo 4 when creating new custom reports, historical data will be archived and old data will be made available for custom reports (as well as Funnels and User flows reports).

By default, the previous 6 months of data will be archived. This will happen either at the next archiving run or triggered by browser archiving. When using browser archiving, Matomo may become unresponsive while the reports are being processed. If you would like the historical data to be included, you should instead disable browser archiving and configure a crontab to run archiving, please see our guide here: configure automated archiving.

You may want to configure this feature to process more (or less) historical data. Configure the historical data by adding a new INI setting to set the number of months in your config/config.ini.php under the [General] section:

rearchive_reports_in_past_last_n_months = 3

You can also disable this feature by setting the setting to 0. Then only data from today onwards will be processed.