@elidon Almost certainly the original question was referring to the Xiao M0 (Xiao SAMD21) which does not have a LiPo charging chip, and not the BLE Sense.
@derfoh With your design, when you’re switched on but not charging, you’re feeding the battery output (4.2V if fully charged) into the 3.3v supply- so how does that work? Don’t you need a small convertor to drop the battery output to 3.3v first? Also, is it safe to leave that switch ‘on’ while plugged in and charging? (I’m pretty sure this will cause the TP4056 to malfunction, since it will be supplying power to both the battery AND the Xiao and it won’t be able to detect when the battery is fully charged - which could lead to overcharging it, no?)