Yep, RISC-V also has these megapages. 4k is the last-level page size. You get larger pages (4M on 32-bit and 2M/1G on 64-bit) by terminating the walk at higher levels of the page table.
Yes, and Linux. at least historically, has not used them without explicit program opt-in. Often advice is to disable transparent huge pages for performance reasons. Not sure about other operating systems.