Ukrainische Streitkräfte durchbrechen die russischen Linien in der Nähe von Lyman und eliminieren das gesamte Regiment

Nice to hear this.

As a rule of thumb, a regiment is 2,500 to 3,500 soldiers.

However, in wartime, most military organizations aren’t up to their „table of organization and equipment“ strengths. If the way the Red Army fought in World War Two is any guide, I’d expect a Russian regiment at this time in the war and at this relative „hot spot“ of the front to number 800 to 1,000.