I think a lot has gone wrong with this situation - IMO Russia has largely been testing the new US president and things haven't gone as they expected - especially with Biden looking weak over Afghanistan and not pushing back initially against Russia in the way they are used to from the US. It has left Russia with something of a conundrum - they don't really know how to deal with weakness where they expected to be met by strength in a foe who is still formidable. Then it seems like any invasion plan revolved around moving into a Ukraine already destabilised in some fashion, probably via some kind of attempted coup, etc. but the US has called them out on false flag scenarios, etc. which has taken some of the wind out of those sails.
As far as an invasion goes they've only recently put the final bits in place - a lot of equipment was built up but it has taken until recent days to get some of the strategic level assets operational, amphibious assault elements moved into the Black Sea, etc. if things are going to kick off it will likely be within the coming days as they aren't going to go to the efforts of having a lot of this equipment setup longer term and having some of the mercenary groups just sitting around indefinitely, etc.
Oh interesting - I only checked Google. Someone had gone to quite some effort on Google LOL.