In the link posted above by @kiwifergus Kueda states :
“accuracy varies considerably by taxon, from 91% accurate in birds to 65% accurate in insects”.
Making the latter part bold, as there are 90000 or so species of insect in N.America but only 2000 or so bird species, so, arguably the 65% accuracy is the more relevant end of the benchmark. This is in a N.American context I think also(?), so likely less accuracy in most other locations.
Meanwhile I´ve seen the museum comment raised by @fffffffff and @dianastuder repeated many times elsewhere - but as far as I saw when I last looked into this, it just seemed to stem from an anecdotal comment/supposition …its not in connection with any actual figures. In the link posted above by @tiwane the only mention of museum quality seems to be in an offhand comment by TonyRebelo.
I struggle to believe any respectable museum insect collection would have a comparable 65% accuracy.
Not that I think iNat is doing a bad job! Its clear its come on leaps and bounds in UK obs this last year. But, there does seem to be a bit of an echo chamber around some of these stats and statements on the forum…which is problematic.