Thanks to @NeshireChoir I finally got the Rasterops Accelerator a 12" NuBus card. Looks like Rasterops made 2 versions, I and II in the same year (1990). I have version I and found quickly what was wrong with version I. It was not designed to be put into compact Mac II like IIcx or IIci. The top...
hm, me too never heard or read about bracket ... the above link doesn't open for me. I had it in Q700 and Q950 in vertical position, never had problems with it. Anyway you need to shut down to turn the card ON/OFF, simple restart does not work.
Well the beta 7.7 is already available here:
https://www.macintoshrepository.org/8155-mac-os-7-7-beta-7-7a2c5-a-k-a-8-0a2c5-
More info here
https://apple.fandom.com/wiki/Mac_OS_7.7