Delibird is not viable in Sh/Sw. It's Defenses aren't good at all. It can't really hit that hard. Most of the moves it gets that actually deal damage are physical. It gets some special moves, but having lots of physical moves on a Pokemon with a measly 55 base Attack just isn't that great. It's Special Attack isn't as great either, only having a base 65 Special Attack. It's best stat is its speed, which is 75. However, 75 base Speed isn't really that great. It isn't good to have a fast Pokemon that can't hit hard. You could try to run Focus Sash, Destiny Bond on it, but it's better to have a Pokemon that can KO an opponent without getting taken out too.
Additionally, there are just better options out there. There are Ice types like Mamoswine, who can deal massive damage, or Zen mode Galarian Darmanitan, who has massive HP, is speedy, and and hits hard. Of course, you need to get a Galarian Darmanitan with it's Hidden Ability, but it sure pays off. Also, there is Arctovish and Arctozolt. They can take some hits and hit back with power. They might not be as fast as Delibird, but the have the bulk to make up for that.
In conclusion: Don't use Delibird. Just don't. It has bad stats, and there are just better options out there. Why use Delibird when you have another Pokemon that is faster and can hit harder or a Pokemon that hits hard and has the bulk to take a few hits. As for competitive, Never use Delibird. You could try to, but the same things from above apply here. There are just better options, and it's stats aren't the best to have.
Hope I helped.