I need to be able to access and change calendars from outlook or ical to be able to work with multiple accounts (incl. work)

Proton Bridge as it stands seems to have some issues due to limited features. For example, no ability to manage the size of the cache means a user with a huge mailbox will end up with a hung bridge. I utterly agree with the CardDAV and CalDAV inclusion - as this would make like so so much easier for people trying to use these apps for business with multiple computers and devices.

I advocate for Proton Mail Bridge to be turned into Proton Bridge and implement CardDAV and CalDAV support. This would be a good start.

Drive via WebDAV for large email attachments might be difficult to implement. File upload and download could be easily handled, but getting a share link is the hard part. We would still need to sign-in to Proton Drive on web browser to generate and copy a share link.

On the other hand, a Drive page on Bridge could allow drag-drop of files which then be uploaded to /attachments or /shared folder in Drive, and generate a share link immediately.

For now my work flow is a mix of Proton Mail, Nextcloud Contacts, Proton Calendar, Nextcloud Calendar and Nextcloud WebDAV. It is sad, but it works. Thankfully Thunderbird has an extension for WebDAV support for large file attachments. Sure it sounds counterintuitive to use encrypted mail + plain file hosting, but at least the generated links are encrypted in email body.

Thunderbird extension for WebDAV support: https://addons.thunderbird.net/en-CA/thunderbird/addon/filelink-provider-for-owncloud/

Especially for Mac OS

I agree with this. I have to rely on nextcloud calendars and contacts sync because Proton Mail bridge is unable to handle calendars and contacts.
I currently have to use a nextcloud server to manage calendars and contacts, because of the lack of this feature (and lack of contacts sync on mobile). It would be much easier to be able to just sync email, calendars and contacts via Proton Mail bridge.