I have followed the steps to add a ssh key on my GitHub account. Now I want to do the same thing and for my BitBucket account. Do I need to
ssh-keygen again for my Bitbucket or can I use the same key that I used for my GitHub?
Common practice is to use the same key for different servers (from one device). If the key gets compromised, you need to replace the key on all the servers.
Using multiple keys requires more complicated configuration and usually does not add much security (when something is compromised, it is usually your computer with all the keys).
It also depends on having or not having the passphrase and the key encrypted.