Availability times not working correctly

Steps to reproduce

Plase watch this first demo (sorry the language is in german):

https://cloud.androidloves.me/s/2XWgo3cnx37gFJH

Some questions about the last view "Zeit auswählen":

• Julis is not available on Tuesday, Saturday and Sunday. The "ganztägig" row has a color on Tuesday, Friday, Saturday, Sunday. This makes no sense. The friday should be free/available
• Julis: also when looking at the 11 and 12 am time slots: Julis is always free (but they should not be free on Tuesday)
• Julis-Test is available on Tues+Wed, but they actually aren't. I don't understand the view at all...tbh

Can this be a timezone issue?

Please watch the second demo. The availablity times were not changed:

https://cloud.androidloves.me/s/eyADxjZ8jT4opG9

This is about the proposals:

• When I add/invite a user, I can't see the free/busy times of the person. I tried it with different users.

UPDATE: When checking the browser console, it says

Skipping availability fetch for non-internal participant:
Object { id: Getter & Setter, name: Getter & Setter, address: Getter & Setter, attendance: Getter & Setter, status: Getter & Setter, realm: Getter & Setter, … }
ProposalEditor.vue:960:1

All users have realm: "E", even when I use/add/invite my own nextcloud account.

Also, when I open the Calendar App (/apps/calendar/timeGridWeek/now), the browser console says:

[ERROR] calendar: [Vue error]: Error in render: TypeError: can't access property "scheduleDefaultCalendarUrl", this.currentUserPrincipal is undefined
Object { app: "calendar", uid: "Julis", level: 2, error: TypeError, vm: {…}, info: "render" }

Calendar app version

6.2.2 (latest)

CalDAV-clients used

just using web ui

Browser

Firefox 149.0

Client operating system

Arch Linux

Server operating system

latest Docker AIO

Start by reproducing the two linked demos and inspect ProposalEditor.vue around line 960, especially the availability-fetch condition and participants' realm values. Also trace the Calendar app timeGridWeek view where currentUserPrincipal is undefined. Done means availability and free/busy times match the configured schedules and the reported browser-console errors no longer occur.