iMac 27" 2015: graphical artifacts

Hello. I have some problems with iMac 27 Retina 5K Late 2015. Once about per 4 days, it shows the strange artifacts like on the video. Before that problem happened it had failed to update to Catalina from AppStore. After this try, it was reformatted to a new HFS+ Fusion Drive with clearly installed Mojave. Before the reinstallation was made this iMac worked very slowly with a few graphical apps like Photoshop, InDesign, Illustrator opened simultaneously. I showed on one of the screenshot that such apps got hung off and needed to be force quitted. Also, I’ve attached the SMART of APPLE HDD ST1000DM003 which has no issues though it looks like the hard drive very beat-up and the Apple Hardware Test showed there’s nothing to be worried about.

Also, there can be lags while working with some graphic libraries which contain a huge amount of files that can also indicate the HDD problem.

What can be the cause of the regular happening graphical issue?

Can a hard drive issue cause instability of the video card driver's work if the SMART is OK. If no, is it could be any video chip issues that need to be fixed in a workshop?

Thanks for your help.