Not necessarily. It depends on what is on the eMMC. The order you described would work only if there is a boot loader on eMMC that checks for microSD presence and points there if found.
If however the boot loader on eMMC is dumb and doesn't care about other bootable devices it just runs through, which can be a big issue if the eMMC module cannot disabled or removed from the board.
I faced a similar issue long time ago when I had a pinebook pro in my collection.
The fixed boot order of rk3399 is SPI, eMMC, SD. RK3588 might be similar. This default behavior cannot be altered, only worked around by telling the boot loader, that is going to be flashed to SPI or eMMC, to look for microSD first.