RT Run time license is a deployment license and that requirement of it is different for each OS.
For Phar lap ETS
Yes. If you want to install the Real-Time Engine on a Windows-based PXI or desktop PC then a run-time deployment license must be purchased.
NI will remove support for PharLap for cRIO in the NI 2020 Software Release and for PXI in the NI 2022 Software Release. For more information, you can find the Phar Lap RT OS EOL Roadmap
in the Additional Resources section of that link.
For NI Linux Real-Time
No, deployment licenses for Linux RT will be no-cost. To install the Linux OS on the PXI controller, you could refer to this link. Provisioning a PXIe Controller to the NI Linux Real-Time Operating System