Crash Bandicoot N. Sane Trilogy

There are actually 47 total available gems in this game, but you only have to earn 42 for this achievement (and you'll actually need 45 to have enough for C3 | Accept No Substitutes (20G)). Unlike the first two Crash games, you can actually get the vast majority of the gems on your first run through many levels. Most boxes are much easier to find and destroy than Crash 2 too, making it much easier. And lastly, the color gems are more easily available too: four of the five are simply found on the Death Routes of each applicable level.

Like with the other games, the first order of business is getting all five color gems, because once you have them, you'll have access to every other gem in the game. Here are where to find the color gems:
 

• Level 12, Deep Trouble - Red Gem - progress literally to the very end of the level where the exit portal is, and there's an exclamation point block to hit on the ground. Hit it, then backtrack until you go straight down the vertical bit to find a newly spawned TNT box on the right. Touch it to activate it, then follow the new path to the end to find the Red Gem
• Level 13, High Time - Purple Gem - stay alive until you reach the Death Route platform, then follow the new path to the end to find the Purple Gem
• Level 20, Tomb Wader - Blue Gem - stay alive until you reach the Death Route platform, then follow the new path to the end to find the Blue Gem
• Level 23, Flaming Passion - Green Gem - stay alive until you reach the Death Route platform, then follow the new path to the end to find the Green Gem

As for the Yellow Gem, you'll first need to obtain at least 10 gold relics. Then, go to the center of the hub world and ride the yellow platform down to a secret warp room. In there, use the entrance to Hang 'Em High to enter into a different part of that level. Follow this short path to the end to find the Yellow Gem

With all five color gems collected, there's nothing stopping you from obtaining all of the clear gems. Note that there are no achievements that require you to get all 47 clear gems in the game, only 45, so you can actually skip two. You need both in Future Tense for an achievement, and need each clear gem in each bonus level (Eggipus Rex and Hot Coco) for another achievement. Other than those though, feel free to leave out two gems that are being problematic for you.

Here is a video, courtesy of PS5Trophies, showing all clear and color gems in all levels.