what is the modern way of saying "what a drag" ?

“What a drag” isn’t an outdated phrase. Most, if not all, Native speakers will understand. But if you want alternatives: “This sucks”, “What a bummer”, “That’s an L” (L = “loss” in slang)

What a drag would be understood. You could also say, what a bummer or that sucks.

I'd say "that sucks" or "this sucks"

What a pain in the arse

what a drag doesn’t sound old-timey to me at all

Just to counter all the comments saying it doesn’t sound outdated: it depends on your age, OP. If you’re under the age of say 35, everyone will understand “what a drag” but absolutely no one is saying it. It would sound a bit odd. I would definitely recommend the alternatives others mentioned as well as maybe “that’s lame”.

I think most people would still understand that. An alternative could be “that sucks/this sucks.”

Personally I'm a fan of "whomp whomp"

"This shits fucked"

Well: Square - teenagers in the 1950s, a drag - teenagers in the 1960’s, sucks- teenagers in the 1980’s, bogus - teenagers in the 1990’s … cringe - teenagers in the 2010’s / 2020’s. Soon there’re be another phrase that comes along to deprecate everything that adolescents identify against. You can fixate on particular meanings, but this language is really serving a social function - it’s coalitional language.

the modern way is “what a drag”

If you want to sound Irish, you could simply say “ragin’” Short for something along the lines of “ I would be raging(angry) if that happened to me” but can be used quite casually and doesn’t imply anger. Eg. Person 1: “I missed the bus.” Person 2: “ragin’”

Such a hassle?

It’s a little old fashioned but no one would really bat an eye at it. “This sucks” and “that blows” are probably the things I’d be more likely to say, but there’s nothing wrong with “what a drag” or “that’s a drag”.

Whoever said that is mistaken. It's still in use

It does sound a little outdated to me—I would use "I'm bored", or something along those lines.

‘Cringe’