I'll share my "How to remember everything and not be overwhelmed" experience. Every day, out of nowhere at work and outside, a lot of tasks arise. For example, to call a client to ask a question, to come in after work in the studio to pick up clothes, to remind the accountant to do the bill on the right day, to write a report for last week and 100500 small and large tasks. It is almost impossible to put such information in your head. And it is not necessary! I, for example, write such things in the usual Reminders on the iPhone. Of course, you can use any other software convenient for you, Google Calendar, Trello and others.
On the plus side, the head as a processor can't process more than X threads at the same time and it's very difficult to manage. The solution is to remove unnecessary "threads" of thoughts, fixing them in devices and on paper.
Correction. If you understand that the task is quite voluminous, you do not need to set it as it is. In 90% of cases you will either postpone it (prostration) or ignore it. Decompose tasks, make small steps and mark them in Reminders. For example, the first part of the task may be "to make a plan to solve this task".