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Today I let my battery level drop below 5% so it disabled the flashlight (icon in dropdown menu greyed out), but when I charged my phone again it didn't return to normal.

I cannot click it so I cannot turn on the flashlight, and every camera app shows the message that I should disable other apps that are using camera or flashlight or it won't open.

I'm sure no other apps are opened as I restarted my phone twice and used the option to close all of the apps.

I'd appreciate any help

Please perform a factory reset of your phone and report back. It may be an hardware related issue, we have to rule it out!

So before factory reset the flashlight was working (but only while testing the phone, I was still unable to use it by any app)
And after factory reset nothing changed except from the default camera app disappearing from my phone (it is still not working in other apps, and flashlight in the dropdown menu is still greyed out)

It is definitely an hardware fault. You'll have to contact your seller to have it replaced / repaired under warranty.