TARGIT has for some time warned that support for 'classical' reports (reports designed with TARGIT 2018 or earlier) will end for future TARGIT releases.
With all versions of TARGIT 2019 and TARGIT 2021 up until update 3 (inclusive), you have been able to open and work with classical reports. This will end now, with TARGIT 2021 update 3 being the last release where you can do this. Therefore, TARGIT has duly recommended to do a (manual) conversion of old reports to the new report format. You can read about the process here:
In previous 2019 and 2021 versions, it wasn't possible to reuse the Scheduled job that was created for the Classical report. It had to be created anew for new report.
With the TARGIT 2021 update 3 (build 19280) release, you can now redirect the scheduled job from the classical report to the new report. You do this from the scheduled job that has already been set up for the classical report: