Qt5 apps using wrong cursor on Plasma 6 Wayland?

I’ve been running a Plasma 6 Wayland session via kdesrc-build (but still using KDE 23.08 apps) for a couple of days now, and so far most of the bugs I’ve encountered are either known already or I’ve made bug reports for since I have some idea of what component it could be in, except for this one: Qt5 apps on Wayland use the wrong cursor style and size, while GTK apps, Qt6 apps as well as Qt5 apps on X11/XWayland all work fine as far as the cursor goes. The problematic apps end up using the Adwaita cursor theme at size 32, while the rest of the system uses Breeze at size 24.

So, I’m not sure if this is even a Plasma bug or just a configuration problem (since the Plasma 6 is from kdesrc-build, sitting alongside Plasma 5 from the Arch repos, on my daily driver system), and if it is a bug I’m not sure which component to report it in either.

So, any ideas on what could be causing the problem?

So it appears that my Plasma 6 session for whatever reason isn’t setting the XCURSOR_THEME and XCURSOR_SIZE environment variables, unlike the Plasma 5 session, and setting both made the cursor look as expected on Qt5 Wayland apps too. Alternatively, if the problem is just the cursor theme another way to set the default/fallback is noted here: KDE - ArchWiki

I’d try booting a KDE Neon Unstable ISO to check, but the one I just downloaded (20231105-1121) doesn’t even make it to the desktop, so still no clue if it’s a Plasma 6 bug or just something with my kdesrc-build setup.