In Settings/Voicemail/ODBC Storage of my FreePBX 17.0.28 instance, you can read “These settings are only applicable when Asterisk is compiled with IMAP support” whil author obviously meant “These settings are only applicable when Asterisk is compiled with ODBC support” .
Maybe someone with appropriate edition rights would consider correcting this.
Quickest way to get it fixed is to open an issue on the FreePBX issue tracker or submit a small PR if you’re comfortable, since these text fixes are usually merged fast. In the meantime it’s harmless (just UI text), but you can double-check behavior against Asterisk docs to avoid confusion when configuring ODBC storage.