I moved your questions into their own thread, because they were not really related to the thread where you had originally posted.
If it’s a non-mobile device, then the “PIN” can also contain non-numeric characters, or even be a passphrase.
If you use an all-numeric PIN, then the numbers should be randomly selected (using a CSPRNG or dice), and the number of digits should be four times the number of words in an equally secure passphrase (e.g., you could use a passphrase consisting of 3 random words, or a numeric PIN consisting of 12 random digits).
If you think that the probability of vault data being stolen from your device is 8000 times lower than the probability of the data being stolen from Bitwarden’s cloud servers, then it would make sense to use a 3-word passphrase (or a 12-digit numeric PIN). If you think that the probability of vault data being stolen from your device is 60 million times lower than the probability of the data being stolen from Bitwarden’s cloud servers, then it would make sense to use a 2-word passphrase (or an 8-digit numeric PIN).
Any process running on your computer is free to read the contents of your clipboard — there is no security for these data. If you go to the Settings of your Bitwarden apps and browser extensions, there is a setting that automatically clears the clipboard after a user-defined time delay (e.g., 10 seconds).