Its a bit silly to lock it down to Intel's barebone Arrai 10 GX PAC board when there are better 3rd party ones. Ditto on the Stratix 10 GX/SX boards.
If you want to try out the oneAPI , you can use the Intel FPGA Devcloud for the same,so you don't have to own a hardware for the learning purpose.
Also the oneAPI is not tied to Intel hardware. If a vendor decides , they can have their own customized version of oneAPI suitable to their needs.