Export world feature is already compatible on android, BUT IS HIDDEN FOR NO REASON?! There is a resource pack which makes world export feature available on android. Steps to reproduce are shown in link: https://youtu.be/8huYvT_cTwU

Link for a resource pack that makes export world feature available on android: https://mcpedl.com/import-export-button-unhider-for-mcpe/ (Note: You may need another file manager such as ZArchiver or Total commander in order to import resource pack into MCPE, and export world unhider resource pack may not work in 1.21.40 or newer)

Export world unhider resource pack is not working in 1.21.51 downloaded from google play store, but it works on 1.21.51 downloaded as APK for free from Androidp1.com