Dicey, your tax situation is different from where I live, but some of the overall strategies may apply.
1) Sell any non-registered stock positions that are at a loss, and rebuy after 30 days or switch to similar but different stock / etf. This gets a capital loss to apply against your capital gain.
2) For the large lump sum, max out registered investments this year (done, you are on this!).
3a) Invest in a dividend generating ETF in a non-registered account. Something stable or low tax. Here, with low annual income on your tax return, the dividends are not taxed. What does your dividend tax look like? I am thinking that you may want to start transitioning into FIRE mode, were you are low enough taxable income each year to make a dividend strategy work for your long term income needs.
"Qualified dividends are dividends that meet the requirements to be taxed as capital gains. Under current law, qualified dividends are taxed at a 20%, 15%, or 0% rate, depending on your tax bracket."
3b) Set up a bond ladder. I mean, if you don'thave a business you want to invest in, and you don't need MORE money..why not set up a bond ladder with $40k coming available every year for 10 years, that you spend or renew that year as you like (buy 10 year bonds, of the interest /risk profile you prefer). You can start it to come due the year you plan to retire, and then each year after that. This does generate interest, however, so buy to take advantage of capital gains instead of interest rates for the same yeild, if you can. It is like creating your own annuity, in a way. One that you can sell at any time (for potential loss), but also one that might run out if you don't continually reinvest the overflow into another 10 year bond.
Anyway, this could pay for your annual splurges (Car, vacation, assisted living) over the next 25 years without much management.
Obviously talk to a CPA for your specific tax situation, but these are the ideas that can work for many, that most people overlook because bonds and dividends are not "Sexy" right now, and they are higher income. Most people with investment questions are higher income, actually, so there is little commonly known information for those of us planning to invest and live on less..
I would also hire more help for around your home with your MIL, even if she goes to senior day camp. Maybe even fly in relatives to take care of her while you vacation or something.