The new high resolution game icons (introduced in MC-262684) are not used. The game only uses the 32x32px icon and upscales it with anti aliasing applied which looks quite strange (at least on my machine).
MC-262890
New higher resolution game icons are not used
Open
6
(Unassigned)
Community Consensus
Platform
Normal
UI
1.20 Pre-release 5, 1.20.1, 23w31a, 1.20.2, 23w44a, 1.20.4, 24w07a, 1.20.5
Retrieved
Can confirm