My methods for dealing with writer's block typically fall into two categories; work through it, or work around it. The first method involves staying focused on your main goal. If you have a deadline that you need to meet for a specific piece, then get it done. Accept that your "best work" is equivalent to the best work you can do right now, and just write it. Not everything is always going to feel like it's your best, and sometimes other people will love the stuff that you consider sub-par.

If you're not on a deadline or the above method just won't work for you, you can also work through it by doing some planning. I personally find that even when I can't summon the will to write, I can usually work on the plot outline. Doing so may inspire you to write, but at the very least it will give you ideas to work with when you do find the energy to write. If that doesn't work for you, try writing or plotting a different story, or even just doing some brainstorming for general ideas. To me writer's block usually amounts to a lack of inspiration, so basically you want to find a way to get inspired about the piece you're working on.

If none of the above seems to help, that's when I turn to working around the problem. This generally involves doing things other than writing in order to refresh your mind. Put some time into playing piano (for me it's guitar), for example, or just go for a walk and let your mind wander. When I'm really struggling with writer's block I will usually go for a walk, and while I'm walking I'll decide on a project to work on. When I get home from my walk I sit down in front of the computer and force myself to write SOMETHING. Even if it's 500 words of crap in a silly story I don't care about, getting words out is a step towards getting GOOD words out, so I'll take it.

Overall it does sound like you're being really hard on yourself. One thing you might try is writing a thread (perhaps a quick solo) in which you just focus on getting the words out, not on how good they are. You could then have it judged or submit it to the workshop, and you'll probably be surprised by how positive the feedback will be despite the fact it's "not your best". As a professional writer I almost never have the luxury of making sure my writing is my "best" because there's always another project to move on to. You're a good writer, so anything you write will probably at least be decent by virtue of the fact that you wrote it. Lean into that and focus on getting something done rather than worrying about the quality. You may be surprised by the results.