Strange behavior of `/proc/self/environ` in some shells; what is going on?

5:29   Deface LFI Upload File Via /Proc/Self/Environ 11:34   LFI to RCE via /proc/self/environ 4:41   LFI proc/self/environ 403 bypass 6:59   LFI to RCE via /proc/self/environ 8:38   LFI + proc/self/environ = Deface 11:27   Intranet - TryHackMe - FLAG 3 - /proc/self/cmdline 6:29   LFI uploading shell with /proc/self/environ 1:24   My /proc/self/environ out of sudden is readable 2:10   [Bahasa Indonesia] Local File Inclusion To RCE using /proc/self/environ DVWA 7:11   26. Gaining Shell Access From LFI Vulnerabilities | First Method 3:20   Upload Backdoor with Tamper Data (proc/self metode) 4:00   [LFI] Shelling Through Process Environment 2:30   LFI to RCE.mpeg youtube demo by h4ck3r.in