The man page doesn’t cover combinations of options like -Fazy, but if options start with -, not --, they are a collection of single character options, not long options, like --admin. -Fazy is -F -a -z -y. -admin would be -a -d -m -i -n, whereas --admin is -a.
Note that recently the help menu was reorganized to move all the extra data options into their own section, like on the man page, so in the help menu it’s now more clear that -a goes along with the other extra data options -x -xx and -xxx.
-v8 is everything about the system. -v7 is almost everything. -F is all upper case options except the very verbose -J and -L, plus -s. -F -v8 is silly because -v7 and -v8 are both almost everything, and certainly more than -F. -F is very roughly comparable to -v5, but I don’t think it’s exactly the same, not sure, but -F is about -v5, -b is -v2, and inxi alone is -v0
-F uses a special form of -R and -E, which means if no data is found, no no data found message appears, to avoid clutter.
-a is --admin which also triggers -xxx automatically. -z triggers the main filters, including the --no-host one. It does not trigger the secondary filters, like for disk labels and uuids, those you have to trigger explicitly. -a -xxx has no meaning since it’s redundant, -a covers it.
You don’t have to read the entire man page, you just scroll down until you get to -F/-full, but ‘full’ is actually not correct, -v8 is full, but that’s far too verbose for normal use. In the old days, -F was actually full, all the lines, but more lines were added that were too complicated, so -F is the main useful options, like -b is the main useful minimalist output, and inxi alone is the absolute minimum output to cover a system. I almost never use inxi alone because I don’t find it very useful.
-a in the man is covered extensively because --admin data is by definition complicated and not necessarily user friendly, so the man page does the best it can to explain what is happening on the lines where it changes output.