3/3 next time i install #KDEneon i'll have at least 4 partitions.

1) EFI
2) /boot
3) swap on LUKS
4) / (compressed btrfs on LUKS)

EDIT: apparently i CAN have a #swapfile on #btrfs, after all. [partitions 2) and 3) aren't required, then]

btrfs filesystem mkswapfile --size 4g --uuid clear /swap/swapfile

https://wiki.archlinux.org/title/Btrfs#Swap_file via @sirber (thanks, mate)