Learn Hardcore German: Die Frist ist knapp, doch das lässt sich vermeiden. - The deadline is tight, yet that can be avoided.

aber/doch: simple contrast; verb stays in 2nd position after the conjunction.
jedoch: more formal; behaves like an adverbial connector. If it’s first in the clause, it takes the first slot and triggers inversion: …, jedoch lässt sich das vermeiden.
trotzdem: “nevertheless”; marks <a class="border-b border-dotted border-blue-400 dark:border-blue-500 cursor-pointer text-inherit no-underline" href="/grammar/german/conjunctions/concessive-and-conditional">concession rather than mere contrast: Die Frist ist knapp, trotzdem lässt sich das vermeiden.

Frist: a time limit or period within which something must be done (often legal/administrative).
Termin: a fixed appointment/date/time on a calendar.
English “deadline” usually maps to Frist, not Termin.
Also useful: Stichtag = a specific due date/cutoff day.

Why is it die Frist? What’s the plural?

Frist is feminine: die Frist (Nom. sg.). Plural: die Fristen. Example declension: Nom. pl. die Fristen, Gen. sg. der Frist.

Why is Frist capitalized?

All German nouns are capitalized, so Frist takes a capital F.

What does knapp mean here? Are there alternatives?

Here knapp means “tight/short/limited.” Alternatives:

kurz (short),
eng bemessen (tightly calculated),
knapp bemessen (tightly allotted).
Note: knapp can also mean “barely/just under,” as in knapp 10 Minuten.