Do you have multiple monitors? I tried this on my laptop but wofi does go full screen.

Nope. Laptop with a single screen. It fails only on fractional scaling like 1.5 or 2.25, but it's ok on integers like 1 or 2.

Here is additional config files: (wofi config does not affect, but it here just in case)

.config/wofi/config

key_expand=space
layer=overlay
image_size=64

.config/wofi/style.css

#window {
    font: 24pt monospace;
}

#outer-box {
    margin: 2pt 2pt 2pt 2pt;
    padding: 4pt 4pt 4pt 4pt;
    border: 2px solid black;
}

#img {
    margin-right: 12pt;
}

swaymsg -t get_outputs

Output eDP-1 'LG Display 0x06F9 Unknown' (focused)
  Current mode: 1920x1200 @ 60.001 Hz
  Power: on
  Position: 0,0
  Scale factor: 1.500000
  Scale filter: linear
  Subpixel hinting: unknown
  Transform: normal
  Workspace: 1
  Max render time: off
  Adaptive sync: disabled
  Available modes:
    1920x1200 @ 60.001 Hz
    1920x1200 @ 47.999 Hz
    1920x1080 @ 60.001 Hz
    1600x1200 @ 60.001 Hz
    1680x1050 @ 60.001 Hz
    1280x1024 @ 60.001 Hz
    1440x900 @ 60.001 Hz
    1280x800 @ 60.001 Hz
    1280x720 @ 60.001 Hz
    1024x768 @ 60.001 Hz
    800x600 @ 60.001 Hz
    640x480 @ 60.001 Hz

.config/kanshi/config

profile {
    output eDP-1 position 0,0
}

profile {
    output "Dell Inc. DELL U2723QE FSDZZN3" mode 1920x1080 position 0,0
    output eDP-1 position 1920,390
}

part of .config/sway/config

    seat seat0 {
        # Hide mouse cursor after a period of inactivity
        hide_cursor 3000
        # Cursor size
        xcursor_theme default 48
    }
   output {
        * bg ~/Pictures/pic.jpg fill
        eDP-1 scale 1.5
        LVDS-1 scale 1.35
    }