2018: 5.1 BB/9, pretty terrible but hard to say if it's this is the norm going forward
2019: 4.3 BB/9, significant improvement, still below average, but he's probably an effective pitcher if he's around this level
2020: 7.8 BB/9, shortened season, limited ramp up, completely revamped deliver that backfired etc.
I guess its' a "trend" if you put significant stock into his 2020, but he also bounced back in 2019 and limited walks. So not sure I'm seeing a trend just yet. I'm seeing a guy who had a down year in 2018, bounced back in 2019, and then a combination of extraneous factors and completely botched remodel just makes me want to throw out his 2020 completely as an outlier.
If he posts 2018 walk rates this year, then yeah you could make a case there's a real trend, but it's hard to make a logical inference right now. He's never going to be a guy that posts average to below average BB-rates consistently between seasons, and that's fine if that your expectation of him.