We had a 4yr old petrol VVTi Corolla (45k), that went in to limp mode one day, with a flashing & beeping oil pressure light.
Totally sludged up.
A big issue in the US apparently, not helped by cool running short journeys.
Toyota didn't want to know, (apart from an £8k engine swap).
Someone told me of a company called Forte, who do a range of engine flushes, only available through the motor trade. The chap on their helpline knew his stuff. Told me exactly what steps to take. Oil change, then flush in. Idle for 2 hours. Then drain while hot. New oil in, idle & drain again. Then sump & pick-up pipe off. Good clean out. Rocker cover off, & top end cleaned out. Then a diesel oil in for a few hundred miles.
Got it going again, & was still running fine when we sold at (I think) 80k.
The ops engine is a step further if it's ingested metal.
If it's got swarf in it's galleries it need stripping back to a block & doing properly. Garages don't seem to want to take engines apart these days.