So, my lawyer’s answer is nuanced:
You need to have the investment in-hand at the time of each application for relevant renewal.
It is theoretically possible to let go the investment after the second renewal, if one is going straight to citizenship. BUT if your citizenship is denied, or the application takes longer to process than you might wish (clearly a possibility, as we’ve seen), then you may be forced to either renew your temporary or apply for permanent (since having applied for citizenship does not obviate your need to retain residency). If this happens and you’ve let the investment go, then you’re up a creek without a paddle.
If you are choosing to continue with temporary residence for whatever reason, then you have to hang onto the investment for each renewal.
If you are choosing permanent residence, you can let it go after your application is approved since there is no ongoing requirement to retain the investment. (In theory you could let it go after the application itself, but what if they come back asking for more documentary evidence?)
If you are choosing citizenship and want to gamble on timing, then you can let it go at ~4 years and a bit, since it doesn’t matter for your citizenship app, and your temporary residency doesn’t expire at year 5 - it runs to year 6, it’s just that you can apply for permanent at year 5.
If you are choosing citizenship but don’t want to gamble, you’re left with your options above.
So whatever the headline, in practice on the ground there isn’t a strict 5-year requirement or fulfillment. It really depends on what you’re doing and the timing thereof. And this is accurately reflected in advertising from (IMO) the more reputable establishments - you can get your permanent residency in 5 years, not that you only need to hold an investment for 5 years. One seems to follow from the other but the reader/client is often merely not being disabused of the inferred conclusion as opposed to corrected in detail, I think. I also tend to fear that are now a lot of legal firms in the business that don’t actually have enough relevant experience with the administrative realities to actually know how things work and are themselves making inferences from law and orders than speaking from experience.