Assuming you are using Windows?
I run a 4k at 27" (Iiyama PROLITE XUB2792UHSU-B1) which is excellent but there are some tradeoffs to be aware of:
1. You will need to use fractional scaling in windows to get a display which isn't too large and isn't too small. I run at 150% scaling which is about right. It's unusable at both 100% and 200% scaling.
2. Some apps don't like fractional scaling and will have terrible icons or blurry UI display on windows. This is improving rapidly though. 90%+ applications work fine though!
3. At no point will this ever work acceptably with macOS or Linux if you move in that direction. Really you need a 5k 27" display running at 200% scaling (integer pixel scaling amounts) for those platforms to work.
4. If your T14 has integrated graphics it may push it to the limit in dual display mode. Don't run it in dual display mode or it'll lag terribly. Also beware that your display scaling amount is probably better at 125% on the T14 and 150% on the 4k display which causes some logistical problems switching displays.
Worth looking a the Lenovo ThinkVision P27u as well. That has 27" 4K IPS and a USB-C charger built in. I'd have bought that if it existed instead of the Iiyama or Dell. But it isn't cheap!
It's game changer for me though (work / software development). If I play games on it, which I do, then I run them at 1920x1080 and put up with the monitor scaling it up for me as my GPU (NVidia 1660 GTX) can't cope