Agreed. There is direct evidence--the fingerprint on the murder weapon matches that of the suspect or the dna samples place the suspect at the scene or credible eye witnesses report seeing the crime committed.
And there is circumstantial evidence--large deposits in a bank account without adequate verification of their origin. . .the robber/murderer/rapist was masked and wearing a blue shirt and witnesses observed the suspect, wearing a blue shirt, hurriedly leaving the premises. . .
That classified documents were found in Biden's garage is not direct evidence that he took them and/or put them there, but it is circumstantial evidence.
The appearance that Hunter used his father to bribe or extort a lot of money from foreign officials currently is circumstantial evidence as is the assumption that Biden knew what Hunter was doing. The purpose of a valid investigation--I'm pretty sure Weiss, with his track record, isn't going to do a valid investigation and he is illegally serving in that role anyway--is to determine if there is any direct evidence to corroborate the circumstantial evidence.
But you are quite right. It is all evidence. And there have been many convictions based on circumstantial evidence alone if there was enough of it to remove all reasonable doubt.