Lightroom itself does not reliably let you freely choose any monitor for the secondary display in a 3-monitor setup. This has been a longstanding limitation in multiple Lightroom versions.

A practical workaround is to change the Windows monitor arrangement so Lightroom “sees” the monitor you want as the adjacent secondary display. One reported solution is:

• set the right-hand monitor as the Windows main display
• drag the left monitor’s position in Windows so it sits below the center monitor instead of in a straight row

That way, Lightroom can place its primary window on the right monitor and the secondary window on the center monitor, avoiding the TV. The tradeoff is that mouse movement between screens will no longer be a simple straight left-to-right path; for example, reaching the left display may require moving the cursor downward from the center screen.

So: there’s no clean Lightroom setting for this, but rearranging monitor positions in Windows may give you a usable workaround.