I have enjoyed using the Wundelich Lowered Footpegs on my 2021 R18, and have determined that they are directly interchangeable
only with the round R18 footpegs. Note the single pivot block on part 2 in the footpeg drawing, that fits between two ears on the mounting block. The floorboards are reversed in that the single pivot block is on the mount and the two ears are on the floorboard, I have not determined the drop difference Lowered to Floorboards, but suspect they ae similar. Note swapping the base mounts can have implications with brake reservoir alignment, kickstand stop location, and a little tilt. i ended up with the Wunderlich on my R18, and put the Flattop BMW R18 B front footpegs on my Transcontinental, I dont believe there was a noticeable difference in drop from the floorboards to the flattop BMW footpegs. Indications are that the Classic could be factory equipped with either the 2021 footpegs, or the 2022 floorboards. I did communicate with Wunderlich America a short time back specifically enquiring after the 2022 R18 TC Lowered footpegs, they replied that the engineers were working on new things all the time but nothing definite, so at this point time will tell.
2021 R18 Basic/Classic- when footpegs equipped
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2022 R18 B/Transcontinental (and 2021 Classic) - when front floorboards equipped

2022 R18 B/Transcontinental - when front footpegs equipped
see different kickstand listed for use with 2021 R18 Classic, for either the round footpegs, or for the 2022 floorboard/flattop pegs.
images grabbed from:
https://www.ascycles.com/
note by my reckoning the R18 model years seem to fuzzy a little in the fiche, with R18 at 2020, and the C, B , and TC being 2021, sorta earlier by one year than how the bikes are marketed, except for the C.