Not affiliated in any way with Actual Budget, but I can’t recommend it enough. It’s the FOSS version of YNAB pretty much so if you’re a fan of envelope budgeting it’s a great tool. I’d even say it has quite a few other strengths compared to YNAB (free bank syncing in the EU with more banks supported for example), and you can always be sure that your financial data stays within your reach.
I don’t think one takes into account investment accounts with envelope budgeting, if I’m not wrong. All the accounts in this kind of budgeting should be involved in the budget, to be money that is to be assigned. “Give every dollar a job” kind of style. Money in investment accounts is for the most part saving for savings sake. But I guess people can assign that kind of money as well, e.g. “this is money that I’m investing to be able to buy a house in 5 years”. I’m not an expert on this so you could look up how YNAB does it, or if Actual has any docs on this.