Everything that currently exists was made during the 6 days:
For in six days the LORD made heaven and earth, the sea, and all that in them is ... Ex 20:11 (KJV).
So anything that was made prior to the 6 days, cannot be in existence today without violating this verse.
There can be no physical evidence, such as a fossil or even one molecule, in existence today that was made prior to the 6 days; without violating this verse. Therefore it's impossible for the "gap theory" to have any existing scientific evidence to support it.
For in six days the LORD made heaven and earth, the sea, and all that in them is ... Ex 20:11 (KJV).
So anything that was made prior to the 6 days, cannot be in existence today without violating this verse.
There can be no physical evidence, such as a fossil or even one molecule, in existence today that was made prior to the 6 days; without violating this verse. Therefore it's impossible for the "gap theory" to have any existing scientific evidence to support it.
There are questions that I cannot answer, but that applies to many controversial doctrines. One day, we will know all things. I suspect we'll all be surprised by how little we know. "Puzzling reflections in a mirror" as one version puts it.