I think the most common recommendation is to start with Yakuza 0.

If you care about story, I’d recommend going 0, Kiwami, Kiwami 2, 3,4, 5, 6, 7 (Like a Dragon), Man Who Erased His Name, and then Infinite Wealth (8).

If you specifically want turn-based combat, you can start on 7 and honestly be pretty OK.

If you just want to have an enjoyable time, you can jump in on any side entry, like Judgment/Lost Judgment, Isshin, or this new Pirate one.

Overall, the mainline Yakuza games have an earnest and serious plot, with moments that take it over the top. But all of it is interspersed with moments of random goofiness and levity. My cousins have spent months on Yakuza 0 because they got really into learning Japanese Mah Jong and enjoyed the slot car racing.