Plasma 5.27 testing has started in the [kde-next] repo, see the release today of Plasma 5.26.90 (5.27 Beta). Final release is planned for three weeks from now.
New added is flatpak-kcm.
As always, place kde-next above all in your pacman.conf. If you do not know how to edit pacman.conf, then please don't try to attempt testing betas of Plasma, editing the pacman.conf is the easiest part of this kind of testing.