There is a kernel bug in 6.13.6 (and mesa 25) and up that causes the dGPU to fail to exit sleep mode once it is put to sleep.
there are patches for 6.14 that resolve, but the solution until that hits mainline for you would be to downgrade your kernel to 6.13.5 or earlier
or as a workaround since 6.14 with patches should hit “real soon now™”, reboot and before the dGPU goes to sleep run an app that prevents it from sleeping (i’ve found nvtop to be effective there) that will keep the dGPU awake but it only works while the PC is awake, if it goes to sleep so will the dGPU and you’ll need to reboot to get it back again.
see this thread for more info: Graphics card not available