It's hard to know what you are seeking. What is "decent 4K experience"?
Many have all worked fine for me with desktop/office work on Linux. But I have older Dell monitors that can only do 30 Hz at 4K and I was not bothered by this. And I do not use the internal laptop screen when using an external monitor, so I have no concern for mixed/high-dpi scenarios. I use a 1080p internal display and 4K desktops with identical dot pitch, and see the 4K monitor as just more real estate for exactly the same font sizes I would use on the smaller laptop screen.
I used to use the same monitor model with a desktop NVIDIA Titan X GPU for scientific work. The experience for regular desktop/browsing was identical, and only differed if I launched an 3D app that really had a use for the extra horsepower. I would suggest that no laptop GPU is really going to both drive 4K at good high frame rates comparable to a modern desktop GPU. There will be some inevitable limits due to the thermal/power design. These days, I think more about idle power and quiet operation, and don't miss having the Xeon + Titan X workstation howling in my office.
I have a T495 with a prior generation AMD Ryzen 7 PRO 3700U that has a Vega iGPU. I've driven a 4K TV or a 4K monitor with its HDMI port at different times, with no drama. It is the best performing graphics I have ever used on a laptop, but is of course limited compared to a desktop GPU since it uses the dual-channel system RAM and has less bandwidth. I don't think you'd play a game at 4K with it, but at 1080p it could perform pretty well.
I've driven a 4K display via displayport and Intel integrated graphics in Thinkpads even from 2015 or earlier. I did this on a T440p (which had an NVIDIA GPU that I learned to ignore, favoring the Intel iGPU). I think I even enabled MST to daisy chain two displays off the single displayport as a test once, using two monitors with the appropriate displayport mode settings in their menus.
My wife has used a T460s for years with a 4K monitor. I think that had a displayport and an HDMI port and both worked fine with 4K, though I don't know if she ever tries using them simultaneously.
I assume the newer models are even better. Going all the way back to the T20 and X20, I've never really seen a backwards step with upgrades to subsequent Thinkpad generations, other than realizing most dGPU choices for Thinkpads were anemic and not worth the bother.