Perspective?

• I’m promoting something.
• You’re advertising at me.

There is a connotational difference, but it’s pretty minor. By definition they’re synonyms. Advertise has a more organized corporate vibe, like there’s an underlying implication that there’s money involved. Promote can be more personal.

Advertise with commercial intent. Promote with personal intent.

“Advertise” to me implies a commercial purpose. So for a Lemmy community “promote” sounds more appropriate IMO.

The two words are spelled differently.