KDE : problem suspend/resume

A little swap is always better than none, see → Swap - Manjaro

I cannot say what causes this - but as you state

At the basic level the kernel is responsible for the power state

I suspect ther may be a glitch with the synced kernel build - I cannot say for sure - but I suspect.

The kernel you are using is EOL, it will soon be removed, within 2-4 weeks it depends.

See → [Stable Update] 2024-08-08 - Kernels, Nvidia, Mesa, AMDVLK, Firefox, Thunderbird, Pipewire, Wine - #2 by philm

My suggestion is to sync the latest 6.10 kernel

sudo mhwd-kernel -i linux610

EDIT:
For the sake of verification - I have tested a KDE on bare metal using the same software level as you do and I cannot reproduce your issue.

System used for verification is

System:
  Host: clevo Kernel: 6.9.12-1-MANJARO arch: x86_64 bits: 64 compiler: gcc
    v: 14.1.1 clocksource: tsc
  Desktop: KDE Plasma v: 6.0.5 tk: Qt v: N/A wm: kwin_x11 vt: 2 dm: SDDM
    Distro: Manjaro base: Arch Linux
Machine:
  Type: Laptop System: Notebook product: N14xWU v: N/A
    serial: <superuser required> Chassis: No Enclosure type: 10
    serial: <superuser required>
  Mobo: Notebook model: N14xWU serial: <superuser required>
    uuid: <superuser required> UEFI: American Megatrends v: 1.07.21
    date: 09/24/2019
Battery:
  ID-1: BAT0 charge: 28.5 Wh (88.0%) condition: 32.4/35.3 Wh (91.6%)
    volts: 12.2 min: 11.4 model: Notebook BAT type: Li-ion serial: 0001
    status: not charging
CPU:
  Info: quad core model: Intel Core i7-8550U bits: 64 type: MT MCP
    smt: enabled arch: Coffee Lake rev: A cache: L1: 256 KiB L2: 1024 KiB
    L3: 8 MiB
  Speed (MHz): avg: 899 high: 2796 min/max: 400/4000 cores: 1: 800 2: 800
    3: 400 4: 800 5: 400 6: 400 7: 800 8: 2796 bogomips: 32012
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx
Graphics:
  Device-1: Intel UHD Graphics 620 vendor: CLEVO/KAPOK driver: i915 v: kernel
    arch: Gen-9.5 ports: active: eDP-1 empty: DP-1,HDMI-A-1,HDMI-A-2
    bus-ID: 00:02.0 chip-ID: 8086:5917 class-ID: 0300
  Device-2: Chicony USB2.0 Camera driver: uvcvideo type: USB rev: 2.0
    speed: 480 Mb/s lanes: 1 bus-ID: 1-4:2 chip-ID: 04f2:b649 class-ID: 0e02
  Display: x11 server: X.Org v: 21.1.13 with: Xwayland v: 24.1.1
    compositor: kwin_x11 driver: X: loaded: modesetting alternate: fbdev,vesa
    dri: iris gpu: i915 display-ID: :0 screens: 1
  Screen-1: 0 s-res: 1920x1080 s-dpi: 96 s-size: 508x285mm (20.00x11.22")
    s-diag: 582mm (22.93") monitors: <missing: xrandr>
  Monitor-1: eDP-1 model: AU Optronics 0x403d res: 1920x1080 dpi: 158
    size: 309x173mm (12.17x6.81") diag: 354mm (13.9") modes: 1920x1080
  API: EGL v: 1.5 hw: drv: intel iris platforms: device: 0 drv: iris
    device: 1 drv: swrast gbm: drv: iris surfaceless: drv: iris x11: drv: iris
    inactive: wayland
  API: OpenGL v: 4.6 compat-v: 4.5 vendor: intel mesa v: 24.1.5-manjaro1.1
    glx-v: 1.4 direct-render: yes renderer: Mesa Intel UHD Graphics 620 (KBL
    GT2) device-ID: 8086:5917
  API: Vulkan v: 1.3.279 layers: N/A surfaces: xcb,xlib device: 0
    type: integrated-gpu driver: mesa intel device-ID: 8086:5917
Audio:
  Device-1: Intel Sunrise Point-LP HD Audio vendor: CLEVO/KAPOK
    driver: snd_hda_intel v: kernel bus-ID: 00:1f.3 chip-ID: 8086:9d71
    class-ID: 0403
  API: ALSA v: k6.9.12-1-MANJARO status: kernel-api with: aoss
    type: oss-emulator
  Server-1: JACK v: 1.9.22 status: off
  Server-2: PipeWire v: 1.2.2 status: active with: 1: pipewire-pulse
    status: active 2: wireplumber status: active 3: pipewire-alsa type: plugin
Network:
  Device-1: Realtek RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet
    vendor: CLEVO/KAPOK driver: r8169 v: kernel pcie: speed: 2.5 GT/s lanes: 1
    port: e000 bus-ID: 3a:00.1 chip-ID: 10ec:8168 class-ID: 0200
  IF: enp58s0f1 state: down mac: 80:fa:5b:60:c4:53
  Device-2: Intel Wi-Fi 5 Wireless-AC 9x6x [Thunder Peak] driver: iwlwifi
    v: kernel pcie: speed: 5 GT/s lanes: 1 bus-ID: 3b:00.0 chip-ID: 8086:2526
    class-ID: 0280
  IF: wlp59s0 state: down mac: 1e:8a:2b:95:88:25
  Device-3: ASIX AX88179 Gigabit Ethernet driver: cdc_ncm type: USB rev: 3.2
    speed: 5 Gb/s lanes: 1 bus-ID: 2-1:2 chip-ID: 0b95:1790 class-ID: 0a00
    serial: 0097E316
  IF: enp0s20f0u1c2 state: up speed: 1000 Mbps duplex: half
    mac: 20:7b:d2:97:e3:16
Bluetooth:
  Device-1: Intel Wireless-AC 9260 Bluetooth Adapter driver: btusb v: 0.8
    type: USB rev: 2.0 speed: 12 Mb/s lanes: 1 bus-ID: 1-5:3 chip-ID: 8087:0025
    class-ID: e001
  Report: rfkill ID: hci0 rfk-id: 4 state: up address: see --recommends
Drives:
  Local Storage: total: 2.04 TiB used: 7.43 GiB (0.4%)
  ID-1: /dev/sda vendor: OCZ model: AGILITY3 size: 223.57 GiB
    speed: 6.0 Gb/s tech: SSD serial: OCZ-0DIEL1YFNWZ3UPC2 fw-rev: 2.25
    scheme: GPT
  ID-2: /dev/sdb vendor: Samsung model: PSSD T7 Shield size: 1.82 TiB
    type: USB rev: 3.2 spd: 10 Gb/s lanes: 1 tech: SSD serial: S6YKNJ0W401770D
    scheme: GPT
Partition:
  ID-1: / size: 201.93 GiB used: 7.43 GiB (3.7%) fs: ext4 dev: /dev/sda2
  ID-2: /boot/efi size: 299.4 MiB used: 296 KiB (0.1%) fs: vfat
    dev: /dev/sda1
Swap:
  Alert: No swap data was found.
Sensors:
  System Temperatures: cpu: 52.0 C pch: 43.0 C mobo: N/A
  Fan Speeds (rpm): N/A
Info:
  Memory: total: 16 GiB available: 15.49 GiB used: 1.13 GiB (7.3%)
  Processes: 272 Power: uptime: 19m states: freeze,mem,disk suspend: deep
    wakeups: 3 hibernate: platform Init: systemd v: 256 default: graphical
  Packages: pm: pacman pkgs: 1088 Compilers: N/A Shell: Zsh v: 5.9
    default: Bash v: 5.2.26 running-in: konsole inxi: 3.3.35