I'd recommend installing OpenWrt 21.02.1 for the Pi4B (64-bit or 32-bit, if you haven't already done so.
Then follow this guide for enabling the onboard wifi:
If you're using a dongle, you will need to install the appropriate package (rtl8188eu-firmware - 20211216-1 - RealTek RTL8188EU firmware). Keep in mind that not all dongles support AP mode, and even if they do, the performance may not be particularly impressive. The Pi's built-in wifi will not make a good AP, either, but it should work.