If it's a conflict between the US and large regional powers (eg. Russia, China, India, UK, etc) assuming combatant morale holds it would be a bloodbath on both sides.
Most regional powers now have the ability to manufacture weapons systems and train soldiers up to par with the where the U.S. was in the 1990s and 2000s now, which means our relative power is much less than in the 1990s or 2000s, when the only near peer was Russia.
On the plus side, we are lucky a number of our allies have stronger power projection capabilities now (eg. SK modernization, Japan'a rearmament, Türkiye's military modernization, Poland's modernization, etc).
That said, the Ukraine-Russia War does highlight how bloody a war between near peers can be.