In my session 0s, I remind players that their PCs are going every 6 seconds, so the player should not be spending a lot of time deciding what to do. It is fine if they need time to look up a rule to adjudicate what they decide to do. It is not fine if they waffle back and forth for several minutes on deciding what to do. I have a lot of luck getting people into good habits and avoiding these problems by setting expectations in session 0, and then making sure session 1 is action packed and quick moving with lots of interaction for PCs in combat between their turns (such as shaking ground that requires low DC strength saving throws not to fall over, or other environmental phenomena that make the combat a bit different than your typical out of the box encounter).
For players that still struggle with technology at the table, I speak with them after a session and ask them to use technology only to support the game (use D&D Beyond, etc...) If they fail to do that, I print out their PC for them and ask them to put the technology away before the session. If they still have trouble, we talk about it as a group.
In the end, if a player is indecisive, I offer a suggestion and ask them what they want to do one more time. If they can't decide, I say, "Do you want to do what I suggested, take the Dodge action or do nothing?" If they decide on something else I also accept it, but limiting their options is something unfortunately necessary to keep things moving.
These techniques are the difference between 1 hour combat and a 15 minute combat.