Self training karate?

[aurik]

Train with whatever materials you have available to you! If you aren't comfortable training in a dojo, then there are a plethora of good YouTube videos and books available. As a brown belt, you should be able to discern which videos have quality content and which ones don't.

Another option you may want to consider is private lessons with your previous CI. At the beginning of the pandemic, our CI was offering private lessons at no additional charge to keep things going. One or two private lessons per month from a more senior instructor could certainly help you "tune up" your karate. Something to consider at least.

Again, train with whatever options you have available to you. The key word in that statement is train.

[sensei8]

I understand your plight to the Nth degree, and having said that, you've a solid Kyu understanding already. My concern is that without training under the watchful eye of an instructor, your techniques will stymie because they won't mature, and maturing in one's techniques is paramount to one's effectiveness.

Imho!!

[DarthPenguin]

If you really can't attend in person classes then i would opt for reputable videos.

You mentioned the issue with people exhaling indoors etc. Would any kind of outdoor training sessions alleviate this? Might be possible to get someone to agree to the occasional session outdoors to help check your technique / that you are progressing appropriately.

If you know someone skilled enough (that you trust to give a useful opinion) then maybe you could also video yourself performing the techniques that you have performed and they can give some critique on the performance of them?

Not a substitute for live training of course, and i don't think you could 'rank up', but it would hopefully help you regain some technical skill and then when able/comfortable to train with people in person again you can then work on the timing that comes from sparring