macintosh hd data missing

[madhavs]

HI guys i have 2 startup volumes namely macintosh hd data and macos high sierra which i created. so the problem is my macintosh hd data is runnning bigsur beta and my 2nd is running catalina. my bigsur got a prohibitory symbol and cant be booted up. i did first aid in utilities and everything is fine. so i went to install a new copy without losing my data in it. but unfortunately the catalina version came up and i cant install bigsur on that volume . i mean the startup volume which came was not macintosh hd data and it was the second one( or is i wrong i dont know) will reinstalling catalina fix the prohibitory sign or why is the bigsur not showing up than the catalina