First of all, don't be too hard on yourself, allow yourself some time to reflect on the things you have accomplished and be proud of them.

Also, if you are in Europe use the GDPR as a starting point to ask them to provide any information they have on you including interview feedback, they must comply.

And third and don't get this in the wrong way but you mention several times in this post that you are "a weak candidate from my CV", are you sure you are not giving this vibe to your potential employers?

Honestly, interviewing is hard and there is a lot of asymmetry between candidates and companies specially on this market conditions, my suggestion is (I know it will sound cheesy) but fake it until you make it.