Illegal? Probably no, but treason certainly is. But since he is an extremely visible politician and former chancellor, ties should be investigated thoroughly, and they are not even hidden. He is openly pro-russian even 4 years into brutal war which russia repeatedly declared on all western Europe, including Germany (as in 'we will raise your cities in nuclear holocaust' to quote them).

Nobody actually pro-democratic or sane is getting such generous 'donations', these don't come for free, in russia this is not private matter but fully state controlled and orchestrated.

If you can't connect 2 and 2 form above and publicly available info and see no problem there, I guess its pretty obvious where you stand on topic of russia - vs - western democratic world war currently happening. An attempt to make this 'just another war this is happening everywhere all the time' ain't true if you live in Europe, this is our existential threat and most folks here realize that very well.