My Dell Vostro 3470 Desktop PC has been freezing up of late

I have been using a Dell Vostro 3470 Desktop PC at home for about 6 years. Has been working fine until recently. As Microsoft has decided to discontinue support for Windows 10 in October 2025, I had upgraded (thru Recovery OS option) to Windows 11 about a month ago, so I can get support from Microsoft for few more years (as long as this PC lasts).

Recently, I have noticed that the PC just "freezes" after going into standby / hibernate mode after 15 minutes. I extended display standby to 30 minutes and standby / hibernate mode to 1 hour, but seems this issue remains. Also, after hard-shutdown (pressing power button for 5 seconds) the PC on restart displays error in storage device when I go into Diagnostics (after pressing F12 key at restart). I switched port from SATA-1 to SATA-2 for the Samsung EVO 870 SSD connected to the PC and restart, and it works fine (except it says windows didn't shutdown/restart properly the last time, etc.). 

Not sure if this issue is related to Windows 11 or something wrong with my motherboard, considering it's 6 years old PC. But, when I run diagnostics from Dell website everything shows as "Passed" including for the Samsung SSD.

Has anyone faced this issue in recent times ? Could this be an issue post a faulty update from Microsoft for Windows 11 (which it releases on 2nd Tuesday every month) ?