Good question.
Key Point : Whether it is a new website or an old one,I usually look at the backlink counts of the top 10 competitors for the keyword I want to rank for.
For example,if the top 10 competitors have an average of around 20 referring domains,I would aim for a max of 20 links built over a period of 2 months.
Even with an older website,the target should depend on the competition for that particular keyword.
For a new website,I personally would not rush link building. I would start slowly and build a few relevant links each month.(Never go for more than 10 links for new website in a month.)
In the beginning, I also like to get the website mentioned on platforms such as YouTube,Reddit,social profiles,Trustpilot,and relevant forums. This helps create a more natural looking backlink profile and gets the website moving in the right direction.
The main thing is to study your competitors first instead of choosing an arbitrary backlink number.