What is the status of KWallet development now in KDE? Does it have a developer, that plan to improve it? Main problem for me is missing sync passwords between different Linux systems.

KWallet sync feature was planned many years ago, but still no progress.

Workarounds via manually syncing kwallet.kwl file got more problems, that profit, here is detailed description: https://bugs.kde.org/show_bug.cgi?id=403648

Also there was be plans to implement KSecretService as replacement to KWallet https://community.kde.org/KSecretService but seems it also stopped.

Now Linux have those popular password storage implementations:

• KDE use KWallet that missing sync feature
  
• Gnome Keyring use Secret Service - https://specifications.freedesktop.org/secret-service/
  
• pass, named as "the standard unix password manager" - https://www.passwordstore.org/ with QtPass GUI https://qtpass.org/
  
• KeePassXC https://github.com/keepassxreboot/keepassxc that try to implement support for libsecret/DBus https://github.com/keepassxreboot/keepassxc/issues/1403
  
• Qt apps use QtKeychain as API to access system password storage

If KWallet development was stopped and no plan to improve it, which project we can recommend to select as alternative?

Very late reply, but there’s this: https://invent.kde.org/frameworks/kwall ... quests/11#