LG sets made in 2018-2019 with BOE panels (including but not limited to European markets) are at a high risk of developing a fault with the screen panel/LCD module. The screen appears black, but the backlight behind is on - the 'OFF' state of LCD screens is black (blocks the backlight). Mainboards of these sets have two versions: ones with two wider #1 and #2 LVDS connectors (68 pins each, for BOE panels) or two a little shorter LVDS connectors (60 pins, for LGD panels).

To check if there is a problem with the panel, power on the TV (standby LED turns off) and measure LCD voltage on the 50V SMD capacitor by the #1 LVDS connector on mainboard. If with both LVDS flat cables plugged into the MB you get 0V, but with them plugged out of MB you get 29-30V, then there is a fault in the panel. Unfortunately LG sets made in 2018-2019 with BOE panels - at least on European market - develop fault(s) in panels. As per the service manual for 43UK6300PUE: for BOE panels, the mainboards (and panels) have 68 pin LVDS connectors, as opposed to 60 pins for LGD panels.

Hope this helps: (1) Remove the back cover by prying it out. (2) Disconnect the battery connector carefully, and connect it back. (3) Replace the back cover and connect to charger. When it has at least 5% charge, power it on. To avoid the same happening again, don't try to power the tablet on when the battery is completely discharged. If the battery is near its end of usable life, replace it with a new one.