Some resources, techniques, and concepts that I've been using to help me overcome nerves and such:

Self-Care Checklist

Here's a handy checklist to go through any time you're feeling overwhelmed or unable to do the things you want/need to do. It covers everything from basics (have you had water, protein, and decent sleep?) to things you might not consider (maybe it's time to take a shower?) to health care (time to talk with your therapist? have you recently switched medications?) and even just taking the time to see if this is a temporary problem or something more serious.

Wall of Awful

Part 1 and Part 2
Concept: In between you and the task you want/need to accomplish is a wall built up of negative emotions surrounding that task, which stem from the problems you've had in the past: failure, rejection, disappointment, etc. In order to accomplish your task, you need to find ways to deal with this wall, and some strategies are more productive than others.

And certain conditions, such as ADHD, make it easier to build the walls and harder to deal with them.

(In addition, when you've got ADHD, the Motivation Bridge is harder to cross, so you need to use more techniques than the average person to bridge those gaps.)

I've found that channel to be full of interesting and useful techniques and ways of conceptualizing what's going on in my brain that's making some of these tasks so hard.

Start With This

While this podcast (by the creators of Welcome to Night Vale) is mostly about writing, some of its advice can apply to other projects as well. The episode on Writer's Block points out that it's often just about feeling overwhelmed; Art Is Disposable discusses how to counteract the part of your brain that's insisting that your creation must be Perfect; To Write in a Plague discusses some of the challenges from our current pandemic, but also how this isn't a new problem (even Shakespeare had to deal with it); Speed and Slowness discuss different styles of creation, from trying to crank out a ton of project under a deadline to doing just a little every day and maybe not even caring what the finished project looks like so much as the process of making it, which can still be valuable; and Know Your Limitations points out the benefit of imposing limits on the outcome.

Well worth a listen, especially if you're stuck wondering what in the world you could write; each episode ends with a suggested read/consume assignment and a suggested write/create assignment.