Here is the model I'm using: https://www.lenovo.com/ca/en/p/accessories-and-software/docking/docking_usb-docks-(universal-cable-docks)/40ay0090us

It's the 40ay Universal USB, not thunderbolt. My AMD T14 would only work with thunderbolt in Windows, refused in Linux. No issues with Intel T14s. (We use strictly Lenovo products at work.) So this might be a better bet for you.

The Z16 works with or without the correct power supply, a T480 should be fine with the one that comes with it.

Not sure of your budget, hopefully it's not too much for you.

https://www.reddit.com/r/thinkpad/wiki/newdocks/

40A9 - ThinkPad USB-C Dock Mixed mode USB C dock daisy-chained to an MST hub. It can drive two 1080p @ 60 Hz and 5 Gbps USB ports. ** Warning: ** there's a credit report of the MST chip dying in there.

40AC - ThinkPad Thunderbolt 3 Dock Thunderbolt 3 dock + MST hub. Most of the time, a much cheaper USB-C dock or a competitor's TB 3 dock is a better bang for the buck; this thing is a bit expensive for what it offers. Especially bad purchase for the X2/T laptops because their half Thunderbolt matched with this dock has zero advantage whatsoever over the dual USB-C Pro/Ultra docking stations. In fact, if the Ultra explanation above is correct then the Ultra provides more video bandwidth than this one.

https://www.caldigit.com/usb-c-soho-dock/

Maybe this might be more in your price range?

It really depwnds on how much power you need for your laptop.

glad it worked out for you; I'm still looking for a solution for my problem that doesn't involve throwing everything out and buying Newest & Best.

do you use the LAN port on the dock by chance? and have you tried using the dock's USB 3 port for data transfer while everything's connected?

here's information I've pieced together from multiple sources. it's kinda ancient hardware and not many people are into supporting it, so information found online is often outdated and unreliable.

so, T480s are basically the same hardware as previous T470 with i5-7200u Kabylake chips, same HD620 graphics and are limited to two data lanes for USB Type-C for DP-Alt connections; newer gens have three. this means you can attach a 4K/60Hz display directly to the USB port and that works ~~it uses like 8 Gbps of the port's 10 Gbps~~ (inaccurate, explained in the link at the bottom). but, it won't work through a dock as the additional USB ports on it (as well as audio and LAN) exceed the throughput of them lanes. there's a table somewhere that lists how many lanes and Gpbs you need for different resolutions/frequencies, I'll try to find it; I've just memorized it for my use case.

now, T480s has TB3 (the USB Type-C farther away from the display, with the extended connector) that can do 40 Gbps, but my WD19 dock doesn't, that's why I was looking to upgrade to said WD19TB.

when you connect a TB dock to a TB laptop, a buncha things should happen. first off making sure TB security is off or permissive (in BIOS setup), because TB does DMA and that's needed for security purposes. it's possible you'd have to turn off SecureBoot in order for that to work. finally, granting TB permissions in the OS (Gnome Shell has a TB entry in settings, don't know how Plasma handles that). basically, if the OS doesn't ask you to grant permissions upon connecting, TB isn't used, you're just using USB 3.1 speeds and those aren't enough.

most of this is just speculation on my part, as I don't have first hand experience with TB because I can't afford to go around buying dock after dock until I find one that works; you're in an awesome position if you can try out all those things for free!

now, as to your specific conundrum, not sure those 100+ Hz display modes are supported at all but you'd have to research this for yourself. as a minimal first step I suggest you get a USB Type-C to DP cable or adapter, that supports DP-Alt and try the monitor directly.

edit: here's a bunch of useful info: https://old.reddit.com/r/thinkpad/wiki/newdocks