How can I seal between a concrete patio and a brick wall?

Urethane or silicone caulk are the usual, but there are others that remain flexible. Read some labels at your hardware store. Flexibility is crucial, so don't use latex. If you have a lot of seasonal movement (frost heave), caulk might not be a good idea anyway.

Either match color or go with clear. Use as small a bead as possible and avoid smearing it out onto either surface by cutting a fine, angled point on the tube and pressing firmly.

Urethane caulk would be the go-to product, but hairline cracks are a bit of a problem.

If your crack was, say, 10mm wide and with temperature variations it widens or shrinks by, say 2mm, then that's only +/-20% width variation. Urethane caulk is elastic, so it'll stretch and squeeze and stay in.

However if you have a hairline crack, say 0.5mm wide, and temperature variations make it widen by only 1mm, then that's +200% width, and the caulk won't be able to stretch enough to stay attached to both sides of the gap.

If you want to seal it for cosmetic purposes, then just use caulk. But if you want it to be watertight to prevent water infiltration you really need to know what caused the crack, if it is going to widen in the future or not, etc.