Are they heavily used in modern combat?
They are not in “widespread use” by any definition of the term. They’ve seen action in a handful of engagements out of tens of thousands of total engagements.
Define "heavy" and "widespread" while you may not see the emphasis on company and battalion level close combat that was seen prior to WWI bayonets remain a standard peice of equipment in modern infantry formations for good reason. Infact I'd wager that knives/bayonets get used more often than hand grenades.