Kee Vault partially supports any KeePass Placeholders within your imported KeePass database.
You should see that the existing placeholder references all work as expected when viewing entries and using Kee to auto-fill forms in websites. Be aware that this is an edge-case for the import process and not regularly tested so there may be bugs (let us know if you find any).
Editing or creating new placeholders is not supported. We have yet to decide exactly what form this support might take or what priority to give its implementation.
Unless you have enabled the option to enable placeholders across your entire KeePass database before importing it to Kee Vault, this option is not available within Kee Vault (as per the original plan to also remove it from KeePassRPC once people have had enough time to migrate to the more secure per-field configuration approach introduced in 2018). You can disable/enable placeholders on an individual field, although doing so is probably not all that useful until we have decided what to do about supporting the creation of placeholders.
Please let us know if you’re interested in us developing more powerful Placeholder support and how you would like this to work (text, diagrams, screenshot mock-ups, etc. are all welcome at this stage - we have no ideas yet so you can play an important role in the feature design if you wish).