Is there a way to add a transfer switch to a main panel that does not have a main breaker? My main breaker is outside near the meter. I would like to have all circuits available for my generator. I would obviously have to watch the load but instead of switching over certain circuits to a different panel I would like to just individually turn on certain circuits or off certain circuits. I have included some pictures of my main breaker, main panel and a sub panel.
Two possibilities, and a big problem.
Turn the inside subpanel into a "main" breaker panel
I'm betting that the inside "main" panel is convertible from lugs to main breaker. It is likely fed from lugs off of the actual main panel outside - i.e., protected by the 200A main breaker, so the original installer saved a few $ by not including a main breaker in the inside subpanel. But you can likely (can't tell for sure without more details) convert it to a "main" panel by adding a main breaker. Then you replace a pair of breakers at the top (left or right, depending on how the interlock is designed) with a locked down double-breaker and install an interlock and run cable from the breaker to an inlet for the generator. You can then run any loads using the generator except for the Pool House, Pool Pump, 4 Ton Upstairs A/C and the mystery breaker.
I am pretty sure the mystery breaker is not a feed to your inside big panel because 60A is simply not enough for that panel.
You will need to clear some space in the panel, either by installing some tandem breakers (where appropriate, watch out for MWBC and other issues) or consolidate some 15A or 20A breakers where acceptable to do so (e.g., can't eliminate dedicated bathroom, kitchen, laundry circuits).
Interlock in the Main Panel Outside
Investigate the upper-right mystery double-breaker. If it is not currently connected to anything or is connected to a no-longer-used circuit, replace it with a locked-down double-breaker and install an interlock and generator inlet. You can then use the generator for any circuits.
PROBLEM: GROUND/NEUTRAL MIXING
The big panel inside is wired as if it were a main panel, in that the grounds are placed on the neutral bars. You can only do that in a true main panel. This isn't even a grandfathered "used to be main and now sub" situation, because if it were then there would be a main breaker in the inside panel, and there isn't one. It could also be OK, in some cases, if the outside panel were used solely as a service disconnect, but it has Pool and A/C, so that loophole doesn't work either.
INSTALL GROUND BARS AND MOVE THE GROUND WIRES FROM THE NEUTRAL BARS TO THE GROUND BARS. This is independent of the generator issue - it is a significant code violation.
We can cross off the 6-8-10 circuit style of obsolete transfer switch that we love to hate around here. #1 A transfer switch can't feed 2 panels. #2 A generator can't feed 2 transfer switches.
Now that thing you call a "main panel" is actually a subpanel that is improperly wired for post-1999 subpanels. The main panel is the one with 5 breakers that you are calling "main breaker".
Given your desire to choose any circuit at any time, your best bet is to install a generator interlock out on the "main breaker". You have 4 dead breaker spaces there. The top 200A breaker turns everything off, yes? It's not back-fed (making it a Rule of Six panel)?
As manassehkatz points out, your "Main subpanel" appears to be a "convertible" to which a main breaker can be retrofitted. You don't need a main breaker there for a breaker, but that plus a breaker and a generator interlock would be a cheap way to get a "whole house except for outside loads" transfer switch.
Also your service appears to be overloaded. The "Main subpanel" should have neutral and ground separated and double-tapped neutrals separated. The "sub subpanel" has too many defects to list here.