I just upgraded to 5.2 and there seems to be no way to do bank transfers anymore. There is no menu entry or toolbar button. Everything else related to aqbanking/hbci e.g. downloading account statements works.
This is a packaging issue by your distribution. Although KMM will compile against Qt6, kbanking is not yet fully ported (formally waiting for the gwenhywfar library to be ported) so any distro that builds KMM 5.2.0 against Qt6 will not include aqbanking. The work on the port has begun, but is just not ready. Aside from trying to get your distribution to repackage 5.2.0 against Qt6, you might try an Appimage, flatpack, or snap build.
aqbanking is there and works, just bank transfers are not working. (And I’m using KDE Neon, I hope they know what they are doing with KDE apps)
Sorry - it looks like I completely misread your question, or just replied to a wrong topic. My bad. I’m not aware of any changes in this area, but I don’t use aqbanking/hbci myself.
One thing to check - first look at the plugins page of the Configure KMyMoney… dialog. I assume KBanking will show as enabled, but I also see a separate entry for Online Banking Operations, for SEPA orders. If that is not present, it might be a configuration issue to be raised with Neon. Next I would check your KBanking configuration for anything that looks odd or changed.
I found the problem: In the past I had a toolbar icon in the ledgers view with which I started the bank transfer. That seems to be gone now. But it is still there in the outbox view which I never used in the past so I totally missed it.