My apologies for the late response as I was busy doing something irl, but find wherever you installed osu to and then right click the application. Select
"Open file location" and then look for the folder titled
"data" and go into the
"r" folder. From there, there should be a list of replays that are there in the .osr extension (osu replay file) if they haven't been exported as any play you've submitted will be saved their locally.
The folder is hidden by default though if you don't have hidden folders and files enabled to be seen in Windows. If you're confused on how to that, here's a step by step guide:
1.) Right-click the “Start” button, then select “Control Panel“.
2.) Go to “Appearance and Personalization“, then select “File Explorer Options“.
3.) Click the “View” tab.
4.) Scroll down a bit and change the “Hidden files and folders” setting to
“Show hidden files, folders, and drives“.
From there, you want to find the date and time that you set the replay and open it to see if it's the replay file of the map you're wanting to export. Right click and copy the file and then paste it to the location in which you want it saved in. From there, all you'd need to do next is send the file to yourself through the means of an email, .zip, or .7z file. Once done, open it by double-clicking the file on your Mac or drag the file into osu! and osu! should default to open the file of the replay.
If you don't have osu! on your Mac, you can follow this installation guide by
Technocoder for your Mac OS. Here's also a video showing how to download and open beatmaps with the client you downloaded. If what I said doesn't work for opening the .osr file, this video should help you. You can watch the video here:
https://www.youtube.com/watch?v=nhRv5IW1xx4&ab_channel=Darkn