Check "I am an advanced user (required reading)", enter advanced-settings.html, last line is where you define your own uBlock scriptlets. Then in My Filters define

    *##+js(myscript)

this will inject into every(1) executable context of every page. You still need to hotpatch workers/sharedworkers/webworkers(I disable the last one entirely).

This way you get some of the control over Chrome browser back. Not so fun fact - Google is very against users having the ability to execute arbitrary user defined code, afair Gorhill had a problem with google concerning injectable scriptlets.

(1) of course there are issues, you cant inject into <iframe src="data: https://github.com/whatwg/html/issues/1753 in Chrome :( so you would have to manipulate CSP to disable those.