Fix Open RCT2 cant find RCT1 or 2 install folders:
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If the errors of:
"Unable to load g1.dat"
or
"The specified path contains a Roller Coaster Tycoon 1 installation but this version is not suitable.  Open RCT2 needs a Loopy Landscapes or RCT Deluxe install in order to use Roller Coaster Tycoon 1 assets."

appear, you can still force Open RCT2 to accept them manually by editing the ~/.config/OpenRCT2/config.ini text file by adding the locations to RCT1 and 2 there.

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Source: https://www.reddit.com/r/openrct2/comments/9n4c6i/unable_to_load_g1dat/
Date: January 18th, 2021