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hehe, I found a solution to fix all the issues, replace board with SKR CR6 board, replace display with CR-10-STOCK or BTT TFT35 V3 or similar, build Marlin 2.0.9.1 for it.
You can also download ready built the CR6-Community firmware 6.1 which also has some preliminary support for the stock display, and have announced full support for CR-10 Smart over coming months.
Everything works as expected and print quality is excellent. From completely non functional trash to fully working treasure. UBL bed leveling that actually works while printing and only needs doing once, what more could you want