How to make some apps always float on COSMIC desktop ?

• Create the following file : ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1/tiling_exception_custom
  With the following content : []

mkdir -p ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1 && \
echo '[]' > ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1/tiling_exception_custom

• In between the brackets, add one like per app in the following format : (appid: "", title: ".*", enabled: true)
  With the process name between the first quotation marks, and for each line that is followed by another, a comma at the end.

vim ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/v1/tiling_exception_custom

[
    (appid: "qalculate-gtk", title: ".*", enabled: true),
    (appid: "copyq", title: ".*", enabled: true)
]

• This setting will apply immediately upon saving, without requiring logout/reboot.

Also, here’s the list of apps that always float by default. It can be replaced by creating the same file at ~/.config/cosmic/com.system76.CosmicSettings.WindowRules/tiling-exceptions-custom.ron. Note title (string) turning into titles (array) and enabled not being present.