P: Shared access - allow metadata editing

"When I share an album with other users, they can only see my keywords but are not able to add their own keywords nor are they able to add a rating."

Are you sure they can see your keywords? I know they can if they have an Adobe subscription and they view the shared album in the Lightroom desktop or mobile apps, but I would think most shared album viewing is done through a web browser, and in that mode I'm not able to see the keywords. Are your other users using the web interface or one of the dedicated apps?

Here's another feature request you might wish to vote for: https://community.adobe.com/t5/lightroom-ecosystem-cloud-based-ideas/p-make-all-contributors-able-to-pick-flag-images/idi-p/12972572

To Share Folders: https://community.adobe.com/t5/lightroom-ecosystem-cloud-based-ideas/p-share-folders/idi-p/12240095

Where to find the feature requests you mentioned so we can upvote them? 

When I share an album with other users, they can only see my keywords but are not able to add their own keywords nor are they able to add a rating.

I would like to share my albums with other ppl for review and enable them to add their own keywords, hence suggest this as a new feature.

1. Correct, it is still not possible for the guest/client to add ratings when viewing a shared album. That also applies to most metadata, they can only add "likes" or "comments" to the images in the shared album. There's definitely a feature request for that functionality already on this forum, suggest you add your upvote. The more votes, the more chance Adobe will implement it.

2. Correct, keywords do not sync between LrC and the cloud. That's been the case since cloud syncing was first introduced and Adobe have not shown any sign of a change of mind. That being said, it is possible to do a one-time, one-way transfer of LrC keywords to the cloud....see this blog post: https://www.danhartfordphoto.com/blog/2019/8/LR12-Sync-LR-Classic-Keywords-to-LR-Cloud

3. Again correct, labels are another thing that the cloud apps do not support.

4. Yes, we can only share one album at a time, we cannot share folders. Again, there's a feature request for that here on this forum, please add your upvote to that. Of limited value, there is the possibility to create and share a "Gallery" of selected albums via the LrWeb browser app. The value is limited as only one "Gallery" can be created and shared.

5. Again, that is indeed the case for shared albums.