Would like to add a 14-30 outlet in my garage
What you have here is called a &quot;split bus panel&quot;.   There is no main breaker and as Limo Driver said, it follows the &quot;rule of six&quot; which means it must be possible to cut all power with 6 movements of your hand, you can cut all power with 4, so you're in good shape that way. But the panel is FULL! The 2 &quot;unused&quot; spaces are probably not available because there are connection lugs behind them. A picture of the innards of the panel would be helpful to get better advice.
Also, it's impossible to feed generator power to a panel like this safely unless you get one of those rinky dinky generac transfer switches with individual breakers. The master electricians here prefer a manual interlock on the main breaker so you can power the entire house from the generator, but that's not possible here.
Another consideration would be a sub-panel. You could upgrade the sub-main breaker from 60 to 100 amps, move some circuits to the sub-panel to make room for your 14-30 outlet.  But that's kind of a kludge.  Less expensive than a full panel replacement, but still a kludge.  If it were my house, I'd do a full panel replacement with a 40 space panel.  I also noticed you're in Washington State (me too), and we have our share of wind storms and power outages. So if you do this, you might want to consider  a breaker for the generator and a generator interlock between the generator breaker and the main breaker.