On your behalf, I've done some playing around. There does seem to be a very quick way (i.e. a minute to set up, then just leave it until done), of making all the ignored topics, disappear, if you can accept getting your hands, slightly dirty.
There are a number of utilities, that let you program in mouse movements/presses. Typically a hot-key to start recording, and you do one demonstration of what to do (i.e. one set of keypresses, for one page), then press the hot key, to stop recording.
I find it usually best, to have ALL applicable windows open on a single screen at the same time, otherwise, these utilities tend to get confused and mess up. Pauses, may be necessary, to give the windows time to operate.
So, if you have the appropriate (ignore/unignore) page open, you can set up the mouse utility, to click select all (for that page), and press the remove the selected ignores.
It then seems to refresh itself with a new (another), set of them (25 a time?), so repeat the same button (mouse) sequences.
Summary:
https://www.eevblog.com/forum/profile/Press 'Ignore Topics Options' to get to the right section.
Depending on utility, set the repeat count to 250 or similar.
START OF MOUSE MACRO:::::::::
Press (via utility) the unlabelled, select all on this page, tick box.
Press (via utility) un-ignore topics.
Let the utility go back to START OF MOUSE MACRO::::::::::::
Sit back for several minutes.
Then put up with the fact, it will take several days, for your ignore topics to build up again.