It is difficult to understand with your description what may be the problem. I assume it is mainly due to the installation of pihole. I suggest to verify first your network environment by using a default Raspberry Pi OS (32-bit) Lite. Follow the official documentation to enable SSH (Secure Shell) and WiFi by Setting up a Raspberry Pi headless. This must work and you are able to correct your network environment.
A new wpa_supplicant.conf in the boot partition will overwrite the existing one on the next boot up.
If you have another SD Card available the you can use it to setup your pihole. If it doesn't work then you can boot the RasPi with the default SD Card and attach the pihole SD Card with a USB card reader to it. So you are able to access all partitions on it and modify its configuration files, like etc/wpa_supplicant/wpa_supplicant.conf or what you want.
You do not tell us what operating system do you use to create the wpa_supplicant.conf. If it is MS Window$ then it may be possible that the editor you are using does not store the file with the correct line endings. MS Window$ uses CR+LF (carriage return and line feed, two bytes), Unix uses only LF (one byte). To be on the save side you should ensure that wpa_supplicant.conf only uses LF.