Question: I am using Office Version 2206 (Build 15330.20230), the current version. When I am searching for an email it shows a message that maybe not all results are shown and that it is still indexing 127279 emails, many more emails than I have recieved since the issue occured. When I search for something it only shows results that more than a year old.

This problem occurs only since a couple of days, possibly since the last update from July 06.

Answer: 
As RonJohn wrote, "computer industry, pushed by IBM, standardized on 8-bit bytes for General Purpose computers".

After that, there are internal advantages with using powers of 2 multiples of that - it allows for everything to be aligned when different size collections of bytes are used, and allows different bits of the address to be routed different places - e.g. which cache-line/block/page you want vs. where in the cache-line/block/page. That would require an ugly (and slow) division if anything other than a power of two was used.

For instance, you might have 32 or 64 bit registers, a 64 or 128 bit memory bus, 128 bit or 256 bit cache lines, 512 byte (=4096 bit) blocks on disk, 4096 byte (=32768 bit) pages in memory, etc. As long as these are all powers of two, the boundaries between them will as much as possible be in the same places, and the addresses all get split up bit-wise for addressing purposes, which leads to simpler hardware.

If for example you were to then throw a 25 bit or 48 bit structure in there and wanted to have an array of them, there would have to be either wasted space or you would end up having elements split across cache lines, memory pages etc. and it would take a division using all bits to determine which element an address was in.

The alignment part of this doesn't matter as much as it used to - for instance modern Intel/AMD chips don't have penalties for misaligned data at the byte level, but quite a bit of engineering has gone into that.

It also would work just fine if the lowest addressable unit was some number of bits as long as powers of 2 are used above that - for instance, if a byte was 7 bits, the other values would be 14, 28, 56, 112 ... . Indeed, many older architectures and some more specialized word addressable CPUs like DSPs use different word sizes, particularly if data and program memory is stored separately (Harvard Architecture).
It's coincidence, or just everyone copying everyone else. There is no deep technical reason that the number of bits should be a power of two. (There is a deep technical reason however that the number of possible values is a power of two).

A processor with 24, or 31, or 60 bit words would work just fine. Processors supporting extended precision have an 80 bit floating point type (that would be the x86 processors today and the 68k processors in the past).

When storing bit arrays, you need to divide integers by the number of bits in a word. There you have a slight advantage for powers of two, but an instruction dividing by *one specific* non-power of two integer is quite simple. When you want to pack small numbers into a bit array, it's nice if the number of bits in the small number divides the number of bits in a word, so a 60 bit word would allow you to store 60 bits, 30 x 2bits, 20x3 bits, 15x4 bits, 12x5 bits, or 10x6 bits in a word.

For character encodings, having 12 bit bytes instead of 8 would make it possible to store all unicode code points into two bytes instead of 1, 2, 3 or 4, which would make lots of text processing code faster.

BTW: "RAM chips will have a size that is a (power of 2) bits". Until Apple ships computers with 12GB RAM chips... Again no technical reason for a power of 2. I actually expected 10GB per chip :-)

CDC (the company that Cray left to build Cray computers) had sixty bit words. Very nice to fit four 15-bit, two 15 and one 30-bit, or two 30-bit instructions into one word.