SUMMARY

STEPS TO REPRODUCE
1. Enabling "System Settings/Session/Desktop Session/Session Restore/On login, launch apps that were open:" to "On last logout".
2. Open flatpak Notepadqq 2.0.0~beta (flathub-beta) with multiple tabs, some unsaved.
3. Open flatpak LibreWolf 124.0.1-1 (flathub) with multiple tabs in multiple windows.
4. Reboot to login screen.
5. Login.

OBSERVED RESULT
6. Device Hangs. Many more windows of Notepadqq and LibreWolf will open then before. For T Notepadqq last session tabs, Notepadqq is opening T windows, each containing the T previous tabs. For T tabs from W LibreWolf last session windows, LibreWolf is opening the W previous windows plus many more windows that just contain an empty new tab (It may be opening T windows but hangs before I can find out).

EXPECTED RESULT
*unreported bug exists*
Repeat Steps 1. to 6.
7. Hold down power button for 5 seconds til device loses power.
8. Boot device to login screen.
9. Displayed in the login screen, is either an always present option or present after an incomplete/questionable last boot option to boot into "Rescue Mode" that ignores the Session Restore Settings while in Rescue Mode (or if needed reboot with "systemd.unit=rescue").
10. Disable Session Restore, fixing system without using another device to search for hours for a solution, like entering rescue mode, but none of which actually work to enter Rescue Mode. (Adding "systemd.unit=rescue" to the end of the "linux" line in GRUB didn't work. Using Ctrl+Alt+F2 to run a terminal then using "systemctl rescue" didn't work).
11. Create new account with kde and file a bug report.
12. Wait (for Session Restore fix, then wait for upstream to patch, then wait for my distro plus DE to patch).
*reported bug fixed*
13. Enable Session Restore.
14. Reboot and device doesn't hang.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: bazzite-asus-nvidia:40 (Fedora Atomic 40)
KDE Plasma Version: 6.0.3
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2