I had spent far too much time trying to solve the Pi4 USB conundrum ( see https://rglinuxtech.com/?p=2922 ) but did recently find that the 5.14-rc kernels enabled the USB3 hub, although USB2 still failed to function.    I then updated u-boot to the ‘latest’ version, and now everything (finally..) works as it should, again..:

Updated u-boot to latest (git) version –
VERSION = 2021
PATCHLEVEL = 10
SUBLEVEL =
EXTRAVERSION = -rc1

Compiled, and copied u-boot.bin to /boot/efi/ (named rpi4-u-boot.bin, on my system)

Booted OK (kernel 5.14)
$ lsusb -t
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/1p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/4p, 480M

Plugged USB drive into USB3 port:
usb 2-1: new SuperSpeed USB device number 2 using xhci_hcd
usb 2-1: New USB device found, idVendor=8564, idProduct=4000, bcdDevice= 0.38
usb 2-1: New USB device strings: Mfr=3, Product=4, SerialNumber=5
usb 2-1: Product: Transcend
usb 2-1: Manufacturer: TS-RDF5
usb 2-1: SerialNumber: 000000000037
usb-storage 2-1:1.0: USB Mass Storage device detected
scsi host0: usb-storage 2-1:1.0
usbcore: registered new interface driver usb-storage
usbcore: registered new interface driver uas
scsi 0:0:0:0: Direct-Access TS-RDF5 SD Transcend TS38 PQ: 0 ANSI: 6
sd 0:0:0:0: [sda] 62333952 512-byte logical blocks: (31.9 GB/29.7 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn’t support DPO or FUA
sda: sda1
sd 0:0:0:0: [sda] Attached SCSI removable disk

-unplugged, then plugged into USB2 port:
usb 2-1: USB disconnect, device number 2
usb 1-1.3: new high-speed USB device number 3 using xhci_hcd
usb 1-1.3: New USB device found, idVendor=8564, idProduct=4000, bcdDevice= 0.38
usb 1-1.3: New USB device strings: Mfr=3, Product=4, SerialNumber=5
usb 1-1.3: Product: Transcend
usb 1-1.3: Manufacturer: TS-RDF5
usb 1-1.3: SerialNumber: 000000000037
usb-storage 1-1.3:1.0: USB Mass Storage device detected
scsi host0: usb-storage 1-1.3:1.0
scsi 0:0:0:0: Direct-Access TS-RDF5 SD Transcend TS38 PQ: 0 ANSI: 6
sd 0:0:0:0: [sda] 62333952 512-byte logical blocks: (31.9 GB/29.7 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn’t support DPO or FUA
sda: sda1
sd 0:0:0:0: [sda] Attached SCSI removable disk

So.. all seems to be OK (as it was with kernel 5.9, all that time ago..)

Robert Gadsdon.   September 3rd 2021.