Did a few test fits with my Z690 board, 2 120 mm fans and the 4060 LP.
a) AIO on bottom: yes, in theory, putting a 120 mm AIO on the bottom and flipping the case upside down could work. its a tight fight though, and one might have to use the - official - side-panel extension mod.
b) bottom GPU dweller: moving the GPU to nearly the bottom of the case, one has enough room to put a regular sized 120 AIO and a slim 120 fan on top.
c) crop + paste job / riser-less: rotate the MB, add standoffs or move the whole middle tray to the "front", then cut about a 1 cm from the back, to accomodate the moved MB IO. next, no riser needed, the GPU just sits comfortable in there. Move the PSU to the top or front, preferably using something like the HDPlex GaN, and then either use regular air cooling - should accommodate up to 90 mm - OR go bonkers and continue with a 120 or 140 mm AIO
d) AIO mock up, part #2: Moving the GPU to the bottom, keeping the sandwich setup, together with HDPlex GaN (even 500), one would be able to stuff a 140 AIO inside, too. Slim fan only, but it should work. Maybe needs a bit of a panel offset, eg. 2 - 3 mm. The thinnest 140 AIO that seems to be still available in Europe is the Raijintek Orcus 140 RBW, with 28 mm radiator thickness.
If one where to go for a custom loop, there are at least two 20 mm 140 rads, so this might be a nicer option.
cu, w0lf.