F1 25/26 on PC

The game and the desktop app run on the same PC, so the telemetry goes to the local address.

In-game settings

Settings, then Telemetry Settings.

Install and sign in to the desktop app
Open the Full Push desktop app and sign in. It listens on UDP port 20777 as soon as it runs.
Turn UDP telemetry on in F1 25/26
Open Settings, then Telemetry Settings, and enter the values in the table above (UDP Format 2025 and 2026 both work).
Drive a lap
Start any session. The app shows the live lap, and each finished lap uploads and appears on the website.

Full Push shows no data while you drive: Check the IP address first, then the port (20777) and the format (2025 or 2026). A send rate of 10 or 20 Hz works but gives coarser traces; use 60 Hz.
Windows asked about the firewall and you chose Cancel: Open Windows Security, Firewall & network protection, Allow an app through firewall, and allow the Full Push desktop app on private networks.
Another telemetry tool is already using port 20777: Only one program can listen on a port. Close the other tool, or forward from it to Full Push on another local port.