Neither the following two commands work:
/execute as @e[type=fishing_bobber,distance=..1] run say hi
/execute at @e[type=fishing_bobber] as @a[distance=..1] run say hi
The fishing_bobber cannot detect other entites or be detected by distance
The commands do nothing even if I swim at the same water block with the fishing_bobber.
If taking the distance parameter away, these commands work correctly.
Are your feet in the bobber? Try a bigger distance value.