It doesn’t explicitly say that you can sell (it would be strange if it did, TBH), but it is not listed as a requirement to maintain the investment and AIMA has also clarified that it’s not required.
What was said in the recent webinar hosted by Madalena Monteiro was that you should keep the investment until you’ve been granted the PR just in case of any issues with the application—and either way at the very least you need to have it at the point of application.
There isn’t really a renewal of the PR right per se (you don’t need to qualify again to maintain your PR status), it’s an administrative act to renew the card.
This is the same for the regular PR, by the way. You won’t be asked during the renewal to prove that you have been at least six months in Portugal per rolling three-year period (which is the minimum stay requirement for that permit). It would be up to the state to bring a case to revoke your permit in case they suspect that you’re not meeting the requirement.
You still need to show regular items such as proof of available accommodation (can be a contrato de comodato or similar), no tax/social security debts in Portugal, etc. I believe this goes for both PR types.