Is the customary post-Tarawih Walimah, observed for over 15 years, considered an innovation (bid‘ah), especially if it involves ostentation, seeking people's approval, and fear of their criticism?

Feeding people is one of the good deeds that Islam encourages. Gathering to do so after Taraweeh is not an innovation (bid'ah). What is prohibited is to make it a regular Sunnah or a mandatory act for which one would be blamed for abandoning. A Muslim should be sincere in their actions for the sake of Allah the Almighty. Therefore, feeding people should be purely for the sake of Allah, not for seeking fame or reputation. Food provided by those who compete (in generosity or status) has been prohibited due to the ostentation and boasting involved. However, if the prevailing custom necessitates it to ward off evil from a person, then there is no harm in it.