[Bug]: Primary Calendar selection changes from visibility change

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

I have 2 Calendars in Nextcloud and one has been selected as primary.
If I (willingly or accidentally) toggle the visibility of the primary calendar, the primary calendar changes to the other one. Under calendar settings it will still show the correct one until I reload.

This is a problem, since accepted invites will go into the wrong calendar.

Steps to reproduce

1. set up 2 calendars for your user (cal-A and cal-B)
2. select one as primary (cal-A)
3. toggle visibility of the primary calendar (cal-A)
4. refresh to see changed primary calendar selection in calendar settings

Expected behavior

Primary calendar should be cal-A, but is cal-B

Nextcloud Server version

30

Operating system

Debian/Ubuntu

PHP engine version

None

Web server

None

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response

Start by reproducing the calendar UI steps with two calendars, selecting cal-A as primary, toggling its visibility, and refreshing. Trace the primary-calendar and visibility-selection handling; done when cal-A remains primary after the visibility toggle and refresh, with invites still targeting it.