Sorry, but your assertion it's not the charger because it works with previous phones is the wrong analogy for iPhone 12. The charging coil in iPhone 12 is not in the same spot as it was in previous phones to accommodate MagSafe. That doesn't mean iPhone 12 isn't compatible with Qi chargers. It actually is. But it likely means your current chargers may not position the charging coils properly with the relocated spot on iPhone 12.
We had charging issues when we first got iPhone 12 and 12 Pro Max. After much research, I came to the conclusion my older chargers weren't going to work with iPhone 12. So I bought new chargers and haven't had any issues since. Our new chargers are dual coil and were repositioned to better align with iPhone 12. And this is important, many older chargers don't have higher watt QC 3.0 charging bricks. So my new chargers have 18W QC3.0 bricks. Bam, no issues charging wireless since and it's been over 2 months now.