You need to jungle a few circuit around. Breaker 7&15 paired up on a tandem and 8,20 on a tandem breaker. Then that frees up two spots, which you will have to juggle around to get them next to each other, then add a 2pole whatever for a sub panel. Then go from there. As an electrician, I f’in hate arc faults, at least gen 1, these look like gen 3, but they are code. Also something you may want to bring up to your builder and you electrical authority, when installing a new panel, it is required to leave two spare circuit spots (next to each other) by code (in Ontario). If this is code in your area, then they will have to do the work. That’s the route I would go first. But if that doesn’t work do what I mentioned above.