So... it depends on the implementation, and the table culture.

I played Balteus Battlerager ("Rage" for short (darn short jokes)), a Dwarven Berserker who always opened with open arms and diplomacy. In Ravenloft. Yeah, this worked approximately never. But, when diplomacy inevitably failed, he waded through his foes like they were human (wrong party, but the quote fits). This worked for the table culture, and thus the character worked.

Quertus, my signature academia mage, for whom this account is named, is a (mild) coward. "Run" and "Hide" (or, at least, "take cover behind the largest terrain element / other PC") should be buttons on his character sheet. Given that he's a totally OP Tier 1 Wizard, that and his tactical ineptitude help make his contribution balanced to the table.

Xyzzy was afraid of "Weird Stuff". The first time he encountered "Weird Stuff", he fled. He just assumed the party would be right behind him. They were not. As the party's heavy hitter (and likely best tactical mind), his unexpected absence threw the party, and the GM, who I believe were not accustomed to Roleplaying taking priority over the tactical minigame. This did not work well, but they adapted (and Xyzzy got turned into "Weird Stuff", helping him overcome his fear).

My Sentient Potted Plant... is a potted plant. It considers things like "move under own power" or "push buttons" to be super powers beyond its kin. It literally cannot contribute (outside talking, perhaps thanks to the demigod (someone else's PC) who carried it). This would not fly at many tables (because contribution = 0), but was great fun at the table in question.

So, know your group. Know the table culture, know what is expected of your character. Then ask, does your character match that? If so, great; if not, adjust, or make a new character.

Does the table require your character to contribute? Equally? Does the table allow you to play a character who is a burden? (How) Will your character's goals / desires conflict with the party? Is that conflict treated as a bane or a boon to the group's enjoyment?

Figure out how your character manifests their cowardice, how that will interact with the party, and how that will affect the group's enjoyment.

Hope that helps.