Myanmar Letter Sha

It marks Sanskrit śa inside a written word.

Here, śa is the standard Latin transliteration of the Sanskrit spelling, not a Myanmar word. Myanmar writing grew from a South Indian script related to Brahmi, an old Indian writing system, adapted around the eighth century to write Mon, a language of the region. The earliest known Myanmar-script inscription dates to the eleventh century. Later, the script was used for Burmese, Pali (a language associated with Buddhist texts), Sanskrit, and other regional languages.

Is ၐ the same as ၑ?

No. They represent different Sanskrit letters.

In standard Latin transliteration, ၐ is śa and ၑ is ṣa. The marks distinguish the spellings, so the Myanmar characters cannot be swapped.