Sounds like you're using a low power adapter. I have a few ipad2 that the kids use for things. Even if they have 1% and we plug them in they can be used while they charge.
I'd also suggest lowering the brightness slightly, can make a huge difference to battery drain
Over a decade ago it was common for tablets of any kind to not be able to hold a charge while plugged in when pushed to their limits.
Perhaps with some tablets, but the iPad 2 and first gen shipped with an adapter (20W?) that didn’t allow that to happen, in my experience.
It was a 10W. I ran many system-intensive games and only remember battery drain when using a smaller power brick, but never ran Geekbench on loop to test that.
These iPads I'm using are ipad2, well over a decade at this point
HA on my MacBook occasionally pushes M1 to its limits. I suspect it's the dashboards with too many items.