Nextcloud Appointments: Timezone disparity between web UI and Thunderbird/Merkuro

Steps to reproduce

1. Book an appointment in a Timezone different than your home timezone
2. Check the Calendar webapp. The event should be displayed in your home timezone.
3. On some CalDav clients (Thunderbird/Merkuro), the timezone is displayed incorrectly

Expected behavior

All CalDav clients should show you the event in your home timezone instead of UTC.

Actual behaviour

Some CalDav clients show the event in UTC timezone.

Nextcloud Calendar Web UI: The event was scheduled in Asia/Kolkata, and shows up correctly in my Timezone (Europe/Berlin)

Thunderbird: The event shows up in UTC time

Merkuro Calendar: Same behaviour

However, the event is shown correctly on my home timezone on the iOS calendar.

Calendar app version

4.6.4

CalDAV-clients used

Thunderbitd, Merkuro, iOS

Browser

No response

Client operating system

No response

Server operating system

No response

Web server

None

Database engine version

None

PHP engine version

None

Nextcloud version

No response

Updated from an older installed version or fresh install

None

List of activated apps

No response

Nextcloud configuration

No response

Web server error log

No response

Log file

No response

Browser log

No response

Additional info

No response

Reproduce the appointment flow using a timezone different from the home timezone, then compare the event in the Calendar web UI with its presentation in Thunderbird, Merkuro, and iOS. Inspect the CalDAV event data and timezone handling first; done means affected CalDAV clients display the appointment in the user's home timezone rather than UTC.