May one lean on a bimah (used for a Sefer Torah)?
It is permitted to lean on the Bimah, in particular when learning etc.
In general, one cannot use something set aside to serve a Sefer Torah (or other article of kedusha – tashmish kedusha) for something with a lower level (Megilla 26b), and certainly not for leaning on. The Mishna Berura (154:10) writes that the Bimah (meaning the table on which the Sefer Torah is placed) is a tashmish kedusha, because at times the covering is removed and the Sefer is placed directly on it.
However, a condition can be made whereby the item is permitted for other uses too. This concept is noted by the Terumas HaDeshen (Vol. 1, no. 273) to explain the common practice that people use objects that serve a Sefer Torah for personal use.
Concerning community articles, he notes that “lev beit din matneh aleihem,” meaning that the community (or heads thereof) make an “automatic” condition permitted normal use of items, in spite of their use for purposes of kedushah. By means of this principle he permits placing sefarim on the bimah and leaning on it.
See also Mishna Berura 154:35-36; Biur Halacha to 154:9.