having trouble with macbook pro 2012 graphics problem it flickers when starting

Does an external display show the same issues as the built-in display? If so, then it indicates either a GPU issue or a software issue. If the external display is Ok, then it indicates an issue with the built-in display's LCD panel.

If you have a 15" or 17" model, then you can try to force the laptop to use the Intel GPU instead of the discrete GPU. IIRC the 15" Retina model did have known GPU issues. To force the laptop to use the Intel GPU you can use the gfxCardStatus app.

I see several things in the EtreCheck report.

First off uninstall CleanMyMac by following the developer's instructions. Cleaning apps are not needed on a Mac and usually cause more problems than they solve plus they impact system performance.

Your laptop is only showing a single 4GB memory module. Do you actually have only a single memory module installed or do you have two memory modules installed?

EtreCheck is reporting a failing hard drive. Run DriveDx and post the report here using the "Additional Text" icon which looks like a piece of paper. It is possible you have a defective hard drive SATA cable which is very common in this particular laptop.

The 13" model is not affected by the GPU issue.

Did you check to see if the external display shows the same issue? Does moving the built-in display affect the problem?

To look for possible software issues run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

The DriveDx report clearly shows the hard drive is failing. 80 sectors have already been reallocated plus the Load Cycle Count is getting close to end of life where I've seen drive issues develop (slowness & other odd issues). The G-sense error rate is beyond the expected lifetime value. There are also 5 UDMA CRC Errors which is usually due to a bad cable. The hard drive SATA cable in the 13" MBPro (mid-2012) model has an extremely high rate of failure so you should replace this cable as well as the drive.

If another drive is having issues, then provide the DriveDx report for it as well. Instead of a screenshot you can use the "Additional Text" icon which looks like a piece of paper to attach the report.

Run EtreCheck and post the report here as I described in the previous post in case you have a software issue.