Ok, then I think you need a USB1.1 (only) hub that won’t talk USB2.0+ to the upstream host. There might be another way to ‘force’ a faster 2.0+ hub to slower speeds, but I’m not sure how other than using a USB1.1 host that forces downstream devices into ‘backward compatibility’ mode. Thus, I think you could plug your existing 3.0 hub into a 1.1 hub (or a USB1.1 port on an old enough PC), and then it should fall back to 1.1 speeds. I did find a stack exchange article on forcing slower USB speeds, but the main suggestion was the same as here – use a USB1.1 host controller. However, they did also suggest a USB isolator (by Adafruit) that might help do the trick (and it also isolates the power, but limits it to 100 mA which may or may not be enough to satisfy your USB3.0 hub).
Finally, just be aware – if you are probing on the host/uplink side of the hub vs. on device port directly, you are technically monitoring the host (PC) to hub interface and not the host (hub) to target device. Depending on exactly what you’re trying to do, this might matter to you, as the hub is both a host (connected to the target device(s)) and a device (connected to upstream host/PC). I don’t think everything passes transparently through the hub, and such details could make a difference in what your doing. If you only want to see high-level data/packets and not low-level signals/timing, you could still try Wireshark on USB (as suggested in the other thread) with your existing setup.
PS: Just curious – are you just not wanting to manually unplug/replug in each device being tested? Trying to automate testing/logging, and/or run remotely?