At first blush, this would appear to be a Federal Pacific panel in fairly urgent need of immediate replacement due to known-defective breakers and even bigger issues with the buses themselves (if it was just breakers, those could be swapped, a-la Challenger). However, I see from the sticker that you're in Canada. FPE is a somewhat different deal there. I would still be making plans to replace this panel not least, because it's full, but not quite the same urgency as in the US.
Every breaker in this panel is a "double-stuff". The true spaces are separated by red lines: 1-2 is a space, and it is on the same bus "stab" (actually bar) as 17-18.... 3-4 and 19-20 share a stab... 5-6 and 21-22 share... Etc.
And FPE uses the same "straddle spaces with a 2-pole double-stuff" arrangement as GE does on their Qline panels.
That will be important because of "stab limits" -- you must consider the four (4) breakers that you will be sharing the "stab" (bar) with. Keep that number sensible - e.g. 100A. For instance position the 60A breaker so the breakers on the other 3 corners of the "stab" will be 15A. That will put you at 105A, which is as good as you can do. DON'T put the 60 where it shares a stab/bar with a 40, 30, and 15... That would be 145A, bad idea.
Beware of Multi-Wire Branch Circuits (MWBC)
This house seems to have many multi-wire branch circuits where 2 hots share a neutral. It is absolutely vital these be positioned correctly. Specifically, they must be right next to each other, and straddling two spaces - they must be on opposite poles, and there must be 240V between the two hots. And the handles should be tied, but good luck finding a handle tie for a Stab-Lok!
So for each 120V circuit you are thinking of moving, follow the hot back to the cable where it enters the box. Make sure the hot, neutral and ground are the only wires in the cable. If it's not that way, don't move it!
Move two 120V breakers to the 2 free spaces at the bottom
So, with all that in mind, you can identify some 120V-only (not MWBC) breakers fit for moving to the 2 free spaces at the very bottom. (1 and 17). Choose breakers so the hole you are leaving straddles a red line.
Then you can just drop a 60A double-stuff 2-pole FPE breaker (if that exists?) into the empty space.