Learn Finnish: Yhteys alkaa pätkiä, joten suljen kameran. - The connection is starting to lag, so I will close the camera.

Both can translate to "so" or "therefore", but they belong to different grammatical categories. Joten is a conjunction, meaning it can directly link two clauses together on its own (just like "so" does here). Siksi is an adverb meaning "for that reason". If you wanted to use siksi in this sentence, you would need to add ja (and) to connect the clauses: ...pätkiä, ja siksi suljen kameran.

Where does the verb pätkiä (to lag) come from?

It comes from the noun pätkä, which means "a piece", "a stub", or "a snippet" (like a short piece of string). Therefore, pätkiä literally means "to chop into pieces". When an internet connection or phone call is cutting out, Finns vividly describe it as "chopping up" or "breaking into pieces".

Why is the verb pätkiä in its basic dictionary form? Don't verbs after "start" usually end in -maan or -mään?

It depends on which verb for "start" you use. The verb alkaa is normally followed by the basic dictionary form (first infinitive), which is why we see alkaa pätkiä. If you used a different verb for "start", such as ruveta, you would need the -maan/-mään form (the third infinitive): Yhteys rupeaa pätkimään.

The English translation says "I will close", but suljen is in the present tense. How do we know it's future?