This mod introduces a doorknob that does not need a door.
Craft a doorknob and then use it on any wall to create a temporary doorway. The length of the doorway depends on the material of the doorknob. The faster it mines, the further the doorway will reach. The doorway will not pass through tough materials such as obsidian, unless you have a strong doorknob made out of diamond.
When the doorway is no longer needed, simply close the doorway by right-clicking the door. All blocks will be restored to their former selves and your doorknob can be picked up to make more doorways in the future.
All versions (1.12.2, 1.14.4, 1.15.2, 1.16.5) currently have the same set of features. Version 1.16.5 has an additional doorknob made out of Netherite. I will attempt to maintain the 1.12.2 version but the code is quite different and 1.12.2 is officially deprecated by the Forge folks.
Note: The doorway should be completely safe to use. It will not try to pass through blocks with tile entities, because of the risk of breaking or disconnecting things.