Subm77

The Output from swayidle -d should be similar to the following lines

2025-07-27 01:34:16 - [Line 1078] No config file found.  
2025-07-27 01:34:16 - [Line 463] Using session: /org/freedesktop/login1/session/c4  
2025-07-27 01:34:16 - [Line 1151] No command specified! Nothing to do, will exit  

and the ouput from loginctl should list the session from the second line of the swayidle -d output.

SESSION  UID USER   SEAT  TTY  STATE  IDLE SINCE  
     c4 1000 subm77 seat0 tty3 active no   -    

1 sessions listed.  

If that is not the case you could look into setting up a login manager like greetd.

What is the output of swayidle -d and from loginctl?
You may not be running within an elogind session which could explain the unknown session error.