[Milhouse]

So # 0415 no connection to the DS 214play.
Have # 0813 installed and certificate from Synology DS 214play in the folder
storage / .config / copied. No connection via WebDav to Synology.

Have it on my Windows 10 computer with Kodi tried, no connection
with newer Kodi versions.

The same with FireTV, new versions, no connection with Synology.

So only old versions until # 0407. At Libreelec


I have no clue what to do.

Can someone help me?

Given that it is not LibreELEC specific, in that case the only possibility is the following Kodi change added in #0409:

Build Details:

1. Additional commits/pull requests/changes not yet merged upstream:
   • Added: [pkg] PR:13647 (perma): Verify add-on zip authenticity
     

This PR adds "[curl] Enable SSL certificate validation" which would explain why you can no longer authenticate against your Synology server, which you must now configure with a suitable certificate - I don't know what certificate you have installed in LibreELEC, but I would suggest asking on the Synology website for more assistance, or starting a separate thread as it's not now likely to be a bug, but by design.

Edit: I guess your other option would be to use dav:// rather than davs://, assuming dav:// is supported by Kodi and your server. You were not establishing a secure connection prior to #0409, so dropping the secure connection means you are no worse off than you were originally, but will at least be able to connect. If you really want a secure davs:// connection then you'll need to fix the certificate issue.