@sun I don't know how one would document this. I've seen a few BBC interview videos where the interviewee made this claim (I suppose it must be based on reports from POWs), but yeah.
This includes reports of a group of "Chechnyan volunteers" behind the borderline in Kursk, who quickly retreated, leaving untrained and unmotivated conscripts to face experienced Ukrainian soldiers once it was clear that the conscripts would quickly be swept aside, leaving them to fight.
So you would not insist, e.g., on government reports or orders, I presume. Which is a relief. Well, for a start, the term for the phenomenon you're talking about is "barrier troops". It has been a common practice in various armies throughout history https://en.wikipedia.org/wiki/Barrier_troops
The presumption that the Russian army uses barrier troops in their war in Ukraine is often based on Ukrainian media reports which Western media then reciprocate.
Personnally, if I had to assess the veracity of such claims, I would rather go with Russian reports than with Ukrainian ones. Not that I don't trust Ukrainian sources, but methodologically it seems a better practice to rely on information about Russian army behaviour when Russian sources talk about it.
The Wikipedia article on barrier troops https://en.wikipedia.org/wiki/Barrier_troops has a paragraph on Russian army barrier troops in the Ukraine war ("Russian Ground Forces") covering the years 2022 and 2023. The paragraph has sources, that, e.g., cite the British MoD which calls the use of barrier troops "likely". Perhaps check these sources for your own.