'Winter Banana' apple variety has long been known to be reasonably graft-compatible, long-term, with a number of pear cultivars. Placing an interstem of WB on an apple rootstock - or even on individual branches - can allow you to graft on pear scions and have reasonable success. Likewise, there are some pear cultivars that are known to be graft-compatible with apple.
Someone, somewhere along the line, developed a 'SuperClone' apple rootstock that was graft-compatible with a large number of pear cultivars.
Some pears are 'more compatible' with apple than others.
25 yrs ago, I bought a bundle of row-run pear (P.communis seedling) rootstocks. I grafted one 2 or 3 times the first year, with no success, and the next tree up the row, had a pear graft that took and grew well, but 'woke up dead' the next spring. When those two rootstocks leafed out the next spring... it became evident that they were apple seedlings, not pear.