I've been using the Gmail webpage for tracking my TODOs for like 20 years. The idea being, since I always have the webpage open in the first tab of my browser, and since I'm checking the webpage at least once a day, I never forget it. Every time I check my emails I also see my TODOs. And I can check/edit it from my phone when I'm not at home.

If it's a list of TODOs for the current day or week (e.g. work tasks, watering the plants, etc) I just start a draft and keep the draft open in the UI and update it regularly, then delete it when everything is done. If it's more mid-long term (let's say TODOs for the month, like buying some big stuff, etc), I usually send it to myself with "TODO [3-4 words description]" in subject and keep it in the inbox to be visible until I completed it. If I need to add something else I just reply to the same email.

I think Gmail has actually an integrated TODO widget in its webpage, but I just use emails out of habit.