Hi!
On my case ( ThinkPad L13 Yoga Gen 2 / 20VKCTO1WW ) the issues with modern standby were due to the laptop waking up fully and not suspending afterwards.
Through a Ubuntu Mate post and trial and error, I decided to disable all wakeup sources except for keyboard / USB (XHCI) and power button (SLPB).
On Fedora 38, I’ve a good sleep status with the following script:
$ cat /etc/systemd/system/acpi-wake.service
[Unit]
Description=ACPI Wake Service
[Service]
Type=oneshot
ExecStart=/bin/sh -c "for i in $(cat /proc/acpi/wakeup|grep enabled|awk '{print $1}'|xargs); do case $i in SLPB|XHCI);; *) echo $i|tee /proc/acpi/wakeup;; esac; done"
[Install]
WantedBy=multi-user.target
and
$ sudo systemctl enable --now acpi-wake.service
This way, disabling almost everything including the LID (which I’m thinking it is somehow the source of the problem), sleep issues never happen.
Battery should last 2 or 3 days this way (not a full weekend probably, but overnight will).
NOTE: unrelated, but on Fedora 38 there was a bug where the OS ignored the lid close. Seems to be fixed on Fedora 39 (again, waking up on lid open won’t work since I disabled it with the script above but closing the lid now suspends the system).