At first they outsourced a bunch of super cheap games to random outsourcing firms.
Then they brought it all in-house and didnt have much more success. Monster Hunter Explore is making maybe $30 million a year, and nothing else even registers. The games were largely insufficient quality or too trite compared to modern competition. For example, one of Square Enixs flagship games is Brave Exvius, which is basically a mobilized version of a full fledged Final Fantasy game (and done with partner studio Alik, though as a publisher, so presumably Alim only eats up 20-30% of their profits).
They hypothetically have four new flagship internal mobile games coming out this fiscal year, but its not clear that they havent mostly been canceled (sans Puzzle Fighter).
And then, a couple months ago, they announced plans to sign off their IPs to much more prominent partners, though presumably as a licensor instead of as a publisher this go around, which gets them better games, but a smaller part of the profits. That said, if they actually got good partners (they wouldnt say who), it would still be a notable step up. But again, we really dont 100% know if its licensor vs publisher or if theyre partnered with anyone good yet, and we still dont know what their 500-700+ internal mobile staff are doing right now.