PHP have unbundled the interbase extension as of 7.4 and moved it into PECL. However, the project on PECL has no releases as of yet, and considering the reasons for unbundling and deprecating the extension, and its commit log, I suspect it's quite likely that there will not be any releases at all.
Would it be possible to migrate this driver to PDO? Also, I'm curious about why it wasn't implemented this way from the start.