Become official 'resident' or not?

Whether you are resident or not is a matter of fact, not that it suits you to do so.

Thus if your circumstances dictate you are obliged to apply for residence status unless you change those circumstances, you are obliged to apply for residence.

I hope that answers your question

PS. You do not need to be resident to open a non resident’s bank account.  You do need an NIE,  which is just a fiscal ID number.  I know at least some banks / Cajas will let you open an account without one but as soon as you are able you will need an ID number ( NIE)

What you need is NIE. I would also get a social security number in your case. Due to the lockdown, you won't be able to get any of those at the moment, so.. You can just wait. In the meantime, prepare the documents, you'll need EX-15 form filled.. Some help with this.

Or you spend 15 minutes on a video call to open an account with a virtual bank. The only document needed is your passport and you'll get a Spanish account number. They have excellent customer service on live chat and free calls. The name of the bank is N26 but there are others. Google it