Hubs are sold by port count. Port count is the specification that matters least. Here are the three that decide whether the hub will do what you want.
1. Power delivery, and the number next to it
If the hub occupies your only USB-C port, it has to pass power back through or your laptop runs down while docked. Look for a "PD" port and a wattage. Then note the difference between what the hub accepts and what it passes on: a hub rated 100 W input commonly delivers less to the laptop, because the hub itself takes a share. If your laptop charger is 65 W, a hub passing 60 W will charge slowly under load.
2. The video output, including the refresh rate
"4K HDMI" on its own is not a specification. 4K at 30 Hz and 4K at 60 Hz are different experiences — at 30 Hz a moving mouse pointer looks wrong, and many people notice it within minutes even if they cannot name it. The refresh rate depends on the hub's internal bandwidth, so if a listing says 4K but never says 60 Hz, assume 30.
Also check whether the hub drives a second display at all. Many do not, regardless of how many ports they have.
3. What the data ports actually run at
USB 3.0 moves about 5 Gbps. USB 2.0 moves about 480 Mbps — roughly ten times slower. A "7-in-1" hub frequently has one USB 3.0 port and the rest at 2.0. That is fine for a mouse and keyboard, and painful for an external drive. Read which port is which before you buy, not after.
Two things people discover too late
Heat. An aluminum body is not styling, it is the heatsink. Plastic hubs under sustained load get hot and some throttle.
SD card speed. A card reader built into a hub often shares bandwidth with the USB ports. If you move large files off cards regularly, a dedicated reader is faster than any hub slot.
A simple way to decide
Count the devices you need connected at the same time, then add one. Most people buy for a theoretical maximum, end up with ports they never use, and still lack the one thing they plug in daily.