STP - RSTP while timer cannot be observed

The TC (Topology Change) while timer in Spanning Tree Protocol (STP) is a hardwired internal mechanism that cannot be directly observed. It is indirectly configured by adjusting the hello timer, as the TC while timer is set to twice the hello timer. To check if the TC while timer is active, you can look for the TC flag in the output of the show spanning-tree detail command. If the TC flag is set, it indicates that the TC while timer is currently non-zero. There is no direct method to observe the TC while timer.

https://networklessons.com/spanning-tree/rapid-spanning-tree-rstp/