To have the F9P talking to the teensy you must have his Uart1 outputting NMEA at the same bautrate than the teensy.
It should be 115000 but some versions since a week or two use 480000.
Follow this tread:
I recommend you to play in Ucenter with the F9P configurations, you will have full understanding how it works.
If you don’t want,you can install all from the V5.6.33 prerelease
The teensy would be loaded with “Autosteer_gps_teensy_v5_5” from TeensyModules/Firmware
The F9P would be updated to 1.32 with the .bin then loaded with 1.32 “SingleAntennaRover.txt” in Ublox F9P Configurations