The OnePlus smartphone's personal Wi-Fi hotspot can be configured with its own network name and a password that you set yourself to prevent unauthorized third-party access.
It does not matter what your own hotspot is called or whether the password consists only of numbers or letters in upper and lower case.

Android 10 (OxygenOS 10.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Wi-Fi & network
Step 3:  Tap on  Hotspot & tethering
Step 4:  Tap on  Wi-Fi hotspot
Step 5:  Tap on  Hotspot name
Step 6:  Enter the  Hotspot name  and tap  OK
Step 7:  Tap on  Hotspot password
Step 8:  Enter the  Hotspot password  and tap  OK
  1. Open the Settings
  2. Tap on Wi-Fi & network
  3. Tap on Hotspot & tethering
  4. Tap on Wi-Fi hotspot
  5. Tap on Hotspot name
  6. Enter the Hotspot name and tap OK
  7. Tap on Hotspot password
  8. Enter the Hotspot password and tap OK

OnePlus Instructions