Despite his lack of eloquence and typical update-as-a-legal-declaration style, Trump's rants about vote-counting do raise some important questions. If mail-in voting is going to become a norm, then there needs to be some guidance on how to treat those votes, lest waiting many days for results becomes a norm as well. Or, God forbid, long, confusing, potentially conflicting, and meandering court decisions/cases.
How long after the election date should mail-ins be accepted and counted? How should the votes of people who sent in ballots but then died before the election be counted? What are ways that can improve transportation and processing of ballots by mail services?
Things like that.
With Congress about as evenly-split as possible, this would be a good task for the incoming 117th Congress. Neither party has an overwhelming majority, so radical (and potentially vote suppression) solutions are unlikely to pass. Such a pre-emptive action could provide clear guidance to courts, enhance the security and legitimacy of the American electoral process, and boost the confidence of Americans in the system. In short, such a move would be most prudent and wise by the incoming 117th Congress.