My laptop runs Kubuntu 25.04 currently. 25.04 uses Plasma 6.3, and 25.10 uses Plasma 6.4.
If I upgrade my Kubuntu install, will KDE Plasma be automatically updated with it?
Yes. It will upgrade Plasma.
Since I have AeroThemePlasma installed, will that break if I upgrade?
Can’t say. It (probably) shouldn’t, as the jump in Plasma is not large or major, like going from Plasma 5 to Plasma 6.
However, as a third-party theme/modification, you won’t really know until you test it or see how other people have fared.