I’ve posted a solution here for the app if you still need it
Anyway just pre-create a %appdata%\Roaming\Bitwarden\data.json with just this settings (the rest will be populated by the app at the first time it will start)
{
"global": {
"theme": "system",
"environmentUrls": {
"base": "https://my.btw.server.com",
"api": null,
"identity": null,
"icons": null,
"notifications": null,
"events": null,
"webVault": null,
"keyConnector": null
},
"region": "Self-hosted"
}
}