I was unable to replicate the issue on other operating systems. I tested on Debian, Ubuntu, Fedora, and OpenSUSE, and the synchronization works perfectly. It seems that the issue indeed lies within Guix/GuixSD.
- bug#33584: GNOME Calendar not syncing with Nextcloud CalD... baconicsynergy
- bug#33584: GNOME Calendar not syncing with Nextcloud... Ludovic Courtès
- bug#33584: Testing on other operating systems baconicsynergy
