@ Peer Maybe this can resolve your problem! ;)

Tips
Better if the original objects are Boolean Union and generator vertical line of Cylinder hidden

The complete easy final Process! :)
Of course each closed curve can be Style colorized and Named inside Moi!
for have directly named Layers inside Affinity V1! (no made here)

With this http://moi3d.com/forum/index.php?webtag=MOI&msg=3334.2
you can name automatically some Styles (so futur Layers) as you want
for have something more elaborated than "Default" following! :)
( Calque = Layer in French)

Intersection with a plane of the Imported PDF





else i have refound a Close Multiple Curves Command :)
https://moi3d.com/forum/index.php?webtag=MOI&msg=2752.1