Do Not Disturb is enabled and disabled from the Control Centre.

Low Power Mode is enabled/disabled from iPad settings - or if you have added the control, you can also enable/disable from the Control Centre. From device settings:
Settings > Battery > Low Power Mode - set to ON or OFF as required
You should note that if set to ON, this mode may be automatically cancelled when charging your iPad to full charge.
The "three dots" to which you refer a likely the multitasking button - a feature of recent versions of iPadOS. If your iPad has iPadOS 17/18 installed, multitasking can be completely disabled, or re-enabled, from iPad settings:
Settings > Multitasking & Gestures > [Multitasking]
