Loading bar whilst key is pressed.

I would like to create a door that requires the player to press and hold a key for it to open. Whilst they do this there will be an on-screen indication of the progress they’re making. However, I can’t seem to get this working, and I’ve tried searching online for help, but I’ve been unsuccessful.

The best examples I can think of would be the defusing feature from CS:GO, or unhooking or opening a chest from Dead by Daylight.

You can just add .001 to a variable while the button is pressed and reset to 0 when released.
then trigger the open sequence once the variable reaches a number that works for you.

Because of computational speeds, add world delta every time and when you get above 1 that should have been a second…

Obviously you can use the same variable to drive the UMG by simply filling in or sliding a slider widget. You just have to find what widget works for it.
a sliding bar is nothing but a shell and an image inside it sliding around.