I tried a different kernel, one that I know works with uio_pruss because I'm using it on a different image (4.19.59-bone-rt-r36). In my custom image, though, the /dev/uio* devices aren't showing up. Here's version.sh output on it:
git:/opt/scripts/:[481db95174653ba485cca3797d4bbbe03c0cded0]
eeprom:[A335BNLT000C1626BBBG0552]
model:[TI_AM335x_BeagleBone_Black]
dogtag:[Pocket NC Debian Buster Image 2021-02-01]
bootloader:[microSD-(push-button)]:[/dev/mmcblk0]:[U-Boot SPL 2019.04-00002-gc9b3922522 (Aug 24 2020 - 16:42:18 -0500)]:[location: dd MBR]
bootloader:[microSD-(push-button)]:[/dev/mmcblk0]:[U-Boot 2019.04-00002-gc9b3922522]:[location: dd MBR]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot SPL 2019.04-00002-gbb4af0f50f (Jul 08 2019 - 11:44:39 -0500)]:[location: dd MBR]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot 2019.04-00002-gbb4af0f50f]:[location: dd MBR]
UBOOT: Loaded Overlay:[BB-ADC-00A0]
UBOOT: Loaded Overlay:[BB-BONE-eMMC1-01-00A0]
UBOOT: Loaded Overlay:[BB-HDMI-TDA998x-00A0]
kernel:[4.19.59-bone-rt-r36]
/boot/uEnv.txt Settings:
uboot_overlay_options:[enable_uboot_overlays=1]
uboot_overlay_options:[uboot_overlay_pru=AM335X-PRU-UIO-00A0.dtbo]
uboot_overlay_options:[enable_uboot_cape_universal=1]
pkg check: to individually upgrade run: [sudo apt install --only-upgrade <pkg>]
pkg:[bb-cape-overlays]:[4.14.20210225.0-0~buster+20210225]
pkg:[bb-customizations]:[1.20201105.0-0~buster+20201110]
pkg:[bb-usb-gadgets]:[1.20200504.0-0~buster+20200504]
pkg:[bb-wl18xx-firmware]:[1.20200813.1-0~buster+20200813]
pkg:[kmod]:[26-1]
WARNING:pkg:[librobotcontrol]:[NOT_INSTALLED]
cmdline:[console=ttyO0,115200n8 bone_capemgr.uboot_capemgr_enabled=1 root=/dev/mmcblk0p1 ro rootfstype=ext4 rootwait coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet]
dmesg | grep remote
[ 1.242393] remoteproc remoteproc0: wkup_m3 is available
[ 1.515377] remoteproc remoteproc0: powering up wkup_m3
[ 1.515394] remoteproc remoteproc0: Booting fw image am335x-pm-firmware.elf, size 217168
[ 1.517496] remoteproc remoteproc0: remote processor wkup_m3 is now up
dmesg | grep pru
dmesg | grep pinctrl-single
[ 0.868764] pinctrl-single 44e10800.pinmux: 142 pins, size 568
dmesg | grep gpio-of-helper
[ 0.879941] gpio-of-helper ocp:cape-universal: ready
END