Typically when removing sand or gravel you place torches underneath to quickly drop all the blocks.

I had torches in my offhand and a hopper in my main hand, broke the gravel with the hopper and then right clicked, placing the hopper instead of a torch. The gravel fell and the hopper disappeared.

I moved on until I found a new patch of gravel after mining a few more blocks, broke the gravel with an empty main hand and placed a torch, the torch placed broke the gravel and then converted into a hopper with all the gravel inside

*I looked if anyone else had this issue already, sorry if its a duplicate*