I would do both ends and the middle if you ever plan to run at full brightness white. The traces on the flex can handle about a meter of power distribution before you get heating, so you should be able to so up to 4 meters with ends and a single center point
If you aren’t doing full white brightness for any extended period and you aren’t running long wires to it, you really don’t need to (I’ve run more than that without end pixels pinking out or over heating). But if you decide to, you should cut the positive in the middle somewhere so you don’t make a loop.
@Charity_Stolarz for power as long as the positive rail is all together and the negative rail is all together there is no need to worry about loops. All points connected together by wire or traces can be considered the same node, and there is no problem with having multiple paths to the same point, in fact, it increases reliability as it adds a redundant path in case something fails
@Zeno_Le_Hericy_Z-Inv I’ve experienced a lot of noise when connected that way. Could’ve been the power supply I suppose- but severing the positive fixed it immediately. Also be sure if you are creating a current loop that you are using only 1 power supply and not powering through the micro controller. For this amount of LEDs I would just power through a usb power bank right through the micro controller- but I’m never going 100% bright white on all of them… Because that would be too damn bright and I wasn’t trying to blind anyone:-)