You always come up with strange problems where there are no easy answers. If the engine was low on oil and the turbo in use, it could rob the crank of needed oil to keep it bathed and friction free. From your paragraph, I concluded that the main bearings are toast. Repair requires total disassembly of the block and not worth the effort or dollars.

You probably did not buy this car new, so the previous owner might have driven it without oil for 5 minutes - that's all it takes.

The compression sounds normal for a car that has been a nonstarter, as the gasoline will wash the rings of oil needed to build compression. But because speed of the cranking should have increased due to the lower compression, and, it has gotten slower, the fault is most likely in the main bearings.

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My back feels better when I sit in a Volvo seat