Most likely water damage and/or corrosion caused by the detergent water damaged the logic board. If you can, take it apart again, fully remove and disconnect the motherboard from everything, using a soft bristled toothbrush and 90%+IPA clean the full surface of the motherboard, both sides, and make sure to get any contacts where things plug in. Also get the other components (***NOT*** camera lenses) and their contacts.[br]
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The mystery is why the "hit it to charge" function earlier.[br]
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I am unfamiliar with samsung M-line phones, but I have extensive experience with S-line and A-line, along with Notes, and a few from the J-line. Is this more of a flagship specs/pricetag (i.e. the S20 that released the same year) or more budget device (i.e. the A12 that released the same year)? Something I have noticed with the A-line budget phones specifically is that the connectors aren't as sturdy and robust as on the S-line phones, and more than one of my clients have had motherboards with the connectors simply break off, either in whole or in part, from the motherboard. If you have a magnifying glass or microscope, see if you can inspect the connection where the ribbon cable between the sub board and main board plugs in, and if that connection has any bent/broken pins, or cracks in the plastic, or is coming loose and separating between the motherboard and the plastic connector, that is likely where your problem is from. Really the only way to fix that would be to reattach the same or a new connector via yourself or someone who has microsoldering tools. Though that is just a hunch and I have nothing to support that theory.