Shown is a screenshot of bells placed onto the top halves of slabs and stairs using setblock. There is clearly enough space for the bell to be placed on the specified area of the block, however manually placing a bell on them through the inventory will not work.
Other blocks with a large enough placeable area, such as cauldrons, hoppers, and certain anvil orientations cannot have bells manually placed on them.
This may be considered working as intended, however given the changes to supported block placement on transparent blocks in recent snapshots I'd rather report this just to be sure.
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Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 1.16.5 and 21w08b.
Can confirm in 1.17.1.
Can confirm in 1.19.

Can confirm in 1.19.2.
Can confirm in 20w51a.