Ukraine is simply trying to force Russia to react and hopefully pull troops from the enclaves it holds in Kharkiv or better yet from its offensives in eastern Ukraine. It hasn’t happened yet, so Kyiv keeps pushing until it does.
Previously Ukraine has had to defend its entire border, while Russia could choose where to apply pressure, stripping troops from areas where they believed there was no threat. Now they will have to defend all of it.
The other benefit is forcing Russia to come out of its trenches and move, exposing itself to attack.
Prigozhin’s mutiny showed that most of Russia’s territory was undefended. Kyiv took note.