There is a consideration regarding older vs newer languages. Mechanically, languages create variable blocks for variable allocation purposes, mostly to keep code and data in separate memory ranges. For those O/S cases that allow "code protection" and "data non-execution protection", discrete areas are set aside within the memory allocation scheme of the eventual program's memory so that different memory management hardware settings can be applied to code vs. data. In such cases, code cannot be modified while the program is running and data cannot be executed as though it were code. This defeats a lot of threats that use code-injection or buffer overrun tricks to compromise a program. The first time I personally came across that was in the late 1970s/early 1980s for the VAX/VMS environment and something called p-sections.
But for VBA, we NEVER write "main" programs where data block layout is an issue. Everything we write is a sub or function for which any locally declared variables go on the program stack in something called the Stack Frame. (Doesn't apply to STATIC variables.)
If I try to think about this dispassionately, I have to say that it should not matter which way you go because either way, a DIM / PRIVATE / PUBLIC statement is merely going to allocate a new slot in the stack frame as an offset from the stack pointer (hardware register). In the VBA environment, variables declared at the top of a sub/function don't even exist until you call the function, at which point the stack frame exists with all of those pre-allocated slots. Variables declared in a module's declaration area don't exist either, at least until the module is activated for the first time and thus loaded to memory
Further, since VBA is pseudo-compiled, VBA code is technically data anyway,... data for the p-code interpreter. Therefore, the code/data protection hardware schemes don't apply. In the absence of hardware protection for our VBA code, I don't see a big difference.
I personally try to declare everything at the top of the module or routine entry point, but I can say with some certainty that I do that because in the period when I learned programming, it was a language requirement, as an early way to protect code and data segments from each other. Therefore, I recognize my preference as habitual behavior, ingrained by rote learning at a time when there was no viable alternative. (Yes, I am that old...)
I will keep on pre-declaring rather than in-line declaring because I have developed habits that make documentation easier to write. (Don't have to go looking for declarations, they are all in a bunch.) That is the only advantage I see that specifically applies to VBA code. Note that I think more advantages apply in true-compiled languages - but for VBA, shouldn't be a big deal.