A lot of the crises that crop up in TOS/TNG era could have been resolved/avoided using 21st century tech
Obviously, they didn't know exactly how it would pan out But just from the perspective of now and projecting forward technologically.
- Spock's sacrifice in Wrath of Khan, they could have used a robot to do what he did, or a robotic arm. Given how critical the location was they would likely have something of that nature in the room already. a plot solution to this aspect could be that an EMP was used by Khan or other damage which destroyed robots etc. on the ship, removing the technological solution
- Essentially any scenario where a character has to go into a very hazardous environment such as in Year of Hell in Voyager. Then again given the extent of damage to the ship they could also knock out all technological options.