Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

The period
End punctuation
Punctuation

Use a period to end all sentences except direct questions or genuine exclamations. Also use periods in abbreviations according to convention.

To end sentences

Most sentences should end with a period. A sentence that reports a question instead of asking it directly (an indirect question) should end with a period, not a question mark.

In abbreviations

A period is conventionally used in the following abbreviations.

NOTE: If a sentence ends with a period marking an abbreviation, do not add a second period.

Do not use a period in abbreviations of organization names, academic degrees, states, and designations for eras.