It's hard to find fun games that can be played in the browser nowadays. They definitely do exist, but there's no where near the variety that we used to have when Flash was still a thing.
I loved the days that Kongregate.com was thriving. Today, Armor Games is still up and running. It has quite some gems worth exploring:
https://armorgames.com/games/rating#games
Unfortunately, it's hard to find fun games on mobile as well. Mobiles games are an utter disgrace nowadays. Can you even call them games? They're an optimised engagement loop with some gameplay in between the "buy platinum coins" and "spin to win" popups.
I'm certainly not an expert but I think you're comparing apples and oranges a little.
Js and canvas is a code execution environment, but Flash had a polished authoring environment which I believe made it easier for less-technical people to get stuff happening.
My experience with that is it usually never works, and for whatever reason the games never seem compelling. Not sure why, flash games never had that problem. They were always full games with rich graphics and often a story.
I literally tried to pull up itch while tablet shopping yesterday - the site never rendered on the tablets and the one game I tried about crashed the whole tablet. Audio/video worked fine. I'm sure if I sat down at a high powered beefy windows desktop maybe they'd work - I remember flash working great on 1GHz celeron processors with maybe 1 or 2 GB of memory and windows 95. Html games are still a bunch of nonsense, on average.
I just pulled up "Farmers Stealing Tanks" on my BlackBerry KeyOne and played for a minute. It was playable (though not perfect), and that's on a 5 year old phone with a chipset that emphasized battery life over performance.
It's hard to find fun games that can be played in the browser nowadays. They definitely do exist, but there's no where near the variety that we used to have when Flash was still a thing.