The IRS Operations During COVID-19 web page suggests that you should resubmit your tax return if after six months Where's My Refund does not yet have any information. However, as of a few weeks ago the IRS was still around 6½ months behind in transcribing paper-filed tax returns, so you should probably not resubmit until at least 7 months have passed from the time you mailed your tax return.
If Where's My Refund shows Processing, your tax return has been transcribed and there is no need to resubmit.
