I've tried ripped copies of the games you listed on an AtGames handheld before (via the SD card slot), they're definitely Niutai-developed. If a game has a "© ALL RIGHTS RESERVED" notice without actually listing a company, that's your clue that it's a Shenzhen Niutai production. Of note is that most of the sports games have their controls turned on their side, as they were presumably designed for knockoff Wii Remote controllers (appearing on the Sega Genesis Arcade Motion Dual etc).

Yep, most of the Niutai-developed sports games are motion control titles, though they can also be played with standard controllers by just pressing the C button most of the time.
This basically turns a games like "Joy of Ping-Pong" into "Joy of Mashing C to Win".

Where did you get those ROMs? Did you dump them from the consoles themselves or from the bundle cartridges? I have one of the bundle cartridges, though I can't dump it yet because my OSCR isn't here yet. ~Cherri

Whoops, I just saw your post here after like a year or so. I'm sure I already explained this in an old Reddit thread but I'll reiterate here.
I got the ROMs from all kinds of sources. A good portion of them came directly from the Flashback 2017, which has a hidden USB port that you can use ADB on, while most of them were found from ROM sites. Some of the more recent additions were extracted from full dumps of other systems, like the D-CAT 16 and the Super Arcade 101-in-1 I think it was called.
There's a lot more games that I need to get properly dumped, including all of the ones on the 40 Bonus Games in 1 cartridge that I have, though unfortunately my Retrode won't recognize it. I need to get an OSCR myself.

I did stumble across this on Reddit's r/roms.https://drive.google.com/file/d/12LWvREqx4sga2_lDT9Yir7vWp9zeFIwA/view

Yep, that's my archive! I just recently created this account because despite everything, there's always room for improvement, and I'm currently looking through these forums to try and find more of these games.