Do you have a multimeter? It sounds like the PSU failed.

How many drives do you have ?

Try using this to see which device is the issue https://www.nirsoft.net/utils/usb_log_view.html

Latest bios? What psu ?

On the modem can you see logs?

Tried https://answers.microsoft.com/en-us/windows/forum/all/memory-integrity-cannot-be-turned-on-due-to/93a45c9f-e3cd-49ed-bb89-6f92d2725492 ?

Go offline, using a live Linux USB, backup data, delete partitions in Linux, clean install windows. https://rtech.support/docs/live-sessions https://rtech.support/windows

Use hardware health monitoring software. Third party, popular ones are hwmonitor, hwinfo, and openhardware monitor ( make sure you enable logging).

Does the router show it is losing wan/internet?

Sounds like the drive. You could try it with an adapter, dock, and/or enclosure.

Use an user agent switcher and fake the phone browser

What PSU and how old is the build/components?

This guide https://rtech.support/docs/guides/disposal-transfer.html

Latest PC bios and SSD firmware (checked in magician)?

Try this guide https://rtech.support/docs/guides/hwinfo.html . Check all temps and if any throttling results

Using imgbb.com or similar, please post a screenshot of disk management(make sure the lower pane is fully viewable).

What website? What browser? What extensions? Have you ever installed any security software(including antivirus and vpn)?

You said you did most of this. https://woshub.com/how-to-repair-deleted-efi-partition-in-windows-7/

Specs?

Are you fully updated? Have you ever installed any security software(including antivirus and vpn)?