Glow Lichen cannot be obtained with a silk touch tool. In the latest snapshot 22w14a, sculk vines were made obtainable with Silk Touch, so I don't see why Glow Lichen shouldn't be able to as well. Sculk veins and glow lichen have near indentical behavior, so I don't see why glow lichen is grouped with shear-obtainables rather than silk touch-obtainables like sculk veins are.