How to get write permissions on Linux host from Windows 10 guest, using virtiofs shared folders

I am trying to share a folder from an Ubuntu 20.04.3 host with a Windows 10 build 19042 (20H2) guest, using QEMU 5.2 / libvirt 7.0.0 on the host and virtio-win 0.1.208 (driver 100.85.104.20800 and associated virtiofs service) on the guest. So far I am able to read files in this host folder without problems from the guest. However I can only create/write/delete files if 1. I use a shell (Windows CMD or Cygwin bash) with *Administrator* rights on the guest OR 2. I change the folder permissions on the host, giving write permissions to "other". Neither of these options is acceptable as a permanent solution. I already toyed with various settings for "user" in /etc/libvirt/qemu.conf, including root and the user owning the shared folder (myself), without success. I do struggle to understand what ultimately determines the write permissions on the host folder. I had assumed this to be related to the UID of one of the hypervisor processes, so I do not see why running as Administrator or not on the guest should make a difference. Can anyone shed some light on this? Has anyone been more succesful? For info: The relevant section of the QEMU domain configuration looks like this:

virtiofs requires accessmode='passthrough'.