OK not yet got into doctrine as yet, but in a much stronger position to understand how firebird can be enabled there. I've had more success with
Illuminate on laravel ( keep mixing up the r and v ;) ). I've forked the xGrz\firebird-support build of that driver and added much of the migration tools - why can't they just call it schema management - just struggling at the moment with the autoincrement fields that work so well in ADOdb. I tried to take a short cut and jump straight to FB5's new automagic generate option, but it's not really compatible with other engines and I'm stuck at the moment getting insert to work . I have webtrees2.2.x installing into a firebird database which is a start, although I still prefer my older ADOdb based version of webtrees ;)
I am seeing the same warning on the doctrine-firebird-driver about schema building and understand most of the problems having solved them in ADOdb so long ago and I can pick up that code now to add weight to here.
Having avoided composer for so long and side stepped it on ADOdb I'm finally getting my head around it, but I'm still trying to work out the best way to debug stuff in VSCode while working with the github codebase rather than the composer installed version.
I also need to work out how to add things missing from the main namespace which I've hacked manually at the moment :( It's so much easier when one has a central codebase to work on rather than dozens of third party bits ...