That's the analog method I said... Very sensitive to unexpected impedance changes.
People abuse flux a lot. Once you have the pads clean, use ak almost invisible layer on each pad, do each pin pin in a single operation, quick and efficient.
Avoid those huge blobs I see in most yt videos to compensate their poor soldering skills, reworking the same pin 15 times.
I usually start with no flux, apply solder to a single pad, put the part and solder the pin, doing all the alignment.
Then I put a very small quantity and do all pins in a single pass (when possible).
Don't flood the thing with alcohol, ot the flux will enter the internals. Take a rag, drop some alcohol into it and rub the board. Repeat few times with clean parts of the rag.
It will be pretty clean, and you'll avoid contamination.
Not a problem with most parts, but in switches, connectors, potentiometers... definitely!
Once the flux enter the insides, no amount of alcohol will fully remove it.
For ICs, sure, I also like to flood it and use a brush for the best result.