AMD and GloFlo split in 2009 but AMD wasn't able to start actually manufacturing their chips with other foundries until 2019 when GloFlo got downgraded to only providing the IO die for Zen 2. This is because AMD was contractually obligated to continue using GloFlo for that time as a condition of the split.
Zen 2 is also where Ryzen went from "exciting and competitive, but not top of the line" to actually giving Intel a run for their money in more than just highly multithreaded workloads.
Improved architecture put AMD within striking distance of Intel and the move to TSMC allowed them to pull ahead.
UNtil 2009 to 2016 AMD was free to use any fab as long as GloFo still has something to do. In 2016, AMD had to pay GloFo to NOT use them for some node sizes.
AMD used TSMC for their CPUs (not IO die!) at least for one generation, and TSMC actually dropped the ball that time and AMD went back to GloFo.
Once again, AMD was fabless since 2009 it's a fact, and it's also a fact that it didn't help them at all.
Zen 2 is also where Ryzen went from "exciting and competitive, but not top of the line" to actually giving Intel a run for their money in more than just highly multithreaded workloads.
Improved architecture put AMD within striking distance of Intel and the move to TSMC allowed them to pull ahead.