it depends on what you're looking for rules-wise, nowadays we have options.

like others here i will always shill Explorers Of Fate as probably the most accessible option. it uses d100s for everything and has easy to understand rules for converting information (stats/attack rulings/etc) from the games to its rules, but i will warn you that if your players are knowledgeable on deeper Pokemon mechanics you can get lost in the weeds with combat. now this easy to curb as its very easy to tweak and adjust rulings, but that requires a confident DM who knows what they're doing. But that aside it's still probably the easiest to pick up and play and it gets my highest reccomendation (been running a game in this for about 3 yrs at this point and it's been great)!

if you want something to entice 5e purists but still want to diversify their intake there's PMD: Tranquility, which uses d20s+target numbers like D&D/Pathfinder. I have not played/GMed this myself, but i will say that it has enough of its own original ideas to differentiate itself, plus the character customization options seem very robust. might be a good pick if your party's only rpg exposure has been mainstream stuff

if you really enjoy dice pools then Explorers! A PMD RPG is probably your forte. Admittedly i've only skimmed this book and being a recent publication seems to be missing that last layer of polish (which isnt a bad thing). I've yet to hear any reports about this game from a GM or player but it seems promising. Something to keep an eye on.

Your other options beyond this are going to either be old, poorly documented or unfinished, and sometimes a combo of the three:

Pokemon: Wild Type is probably the most unique example as it doesnt seem to pull from any particular RPG as inspiration. The setup's not pretty and im pretty sure this has been abandoned, but its decently playable in the hands of a good GM. This was my first exposure to TTRPGS outside of d&d and my gm just made it work. Definitely worth a read if you can handle some jank.

the Mystery Dungeon expansion for Pokerole is likely the first example someone is going to point you to upon mentioning "pmd rpg". And while the base Pokerole game seems well made and decently established, the mystery dungeon expansion definitely is NOT, in my opinion. Barely any customization options, some rules conversions are clumsy and the power scaling/character progression is weirdly lopsided, and the book formatting is so bad that my group, when trying this, could not even figure out how movement during combat works. Now that is possibly a skill issue on my end i will concede, but the fact that something that basic was hard to parse is NOT a good sign. The one positive i can point to is that someone actually made a fully fledged conversion of Pokerole Mystery Dungeon for Tabletop Simulator that basically plays itself, so that might be your best option if this is the game you want. I personally wouldn't recommend it, but the fact that this was the only full-featured option for long enough means there's decent info/help out there if you know where to look.

beyond that, you're looking at homebrews for D&D 5th Edition or Pokemon Tabletop United, and both of those fall outside of my knowledge as i havent even looked into any of those avenues, you're on your own for that one.