Straight is an adjective or adverb meaning “direct, linear, not curved or bent, extending from one point to another directly”—like a road without turns. Straight can describe a shape or a manner of travel (direct, without stops or side-trips):
Mountain roads are never straight. (shape/adjective)
We are not going straight to Paris; we go to Madrid first, then Paris. (travel/adverb)
Straight also has many abstract or metaphorical meanings:
Please tell me straight, do you love me? (direct communication)
This quote comes straight from the Bible. (direct source)
I like my whiskey straight. (liquor without soda or other ‘mixers’)
After the accident he began to fly straight. (stay away from crime and drugs)
Strait is a noun meaning “a natural water-way between two pieces of land.” Two well known examples are the Straits of Taiwan (between Taiwan and mainland China) and the Straits of Gibraltar (between Europe and Africa, at the mouth of the Mediterranean Sea).
However, we more often hear the word straits (plural) used metaphorically for “a dangerous situation”—thus the cliché, and name of a great rock group, dire straits, which means “an extremely dangerous situation.” This metaphor is based on the fact that real straits are dangerous for boats:
Between covid and climate change, the world seems in dire straits these days. (in danger)
We do not need two dangers to call it dire straits. Any dangerous situation works.