Dangerous 286: Vintage hardware fireworks!

A 286 board with a 20 MHz Harris CPU from the scrapyard! The board I try to restore is compact and has SIMM sockets! It would be a shame if this board would go to waste - unfortunately, there seem to be a few obstacles in the way. I hope you can help me figure out what is wrong with this board!
Thank you ‪@tony359‬ for trying to help!

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▬▬▬▬ Timestamps ▬▬▬▬▬▬▬▬▬▬▬▬▬▬
00:00 Octek FOX II 256
00:38 Cleanup
02:35 Remove battery
04:07 Apply vinegar
07:14 PCBWay
07:44 Inspect damage
11:45 Remove keyboard connector
15:15 Clean board from corrosion
18:52 Fix traces
24:28 Fix charging circuit
28:38 New keyboard connector
31:38 Configure board + manual
38:00 First test
38:45 Replace tantalum remains
41:30 Second test
42:00 I need your help
46:34 Thank you