I have done just what you are talking about.  There is still an isidous
flaw in the install program.
I used the manual / custom to install almaLinux. 
The problem:
When you setup your system manually and tell it not to format a disk but
just mount it.  It all looks good but when you finish the install all
data on all disks is gone.  Including the disk with the .iso and two
disk containing image of our system.  Thank god for a backup on SL 6.5.

This same problem exists in Mint 20 and other derivatives after 7.0
Mint is even worse if remove a file from the desk top, reinstall it,
remove it and your complete server is erased.
In spite of a number of complaints - and examples that can be reproduced
no one seems to be concerned.
We did not use almalinux 8.3, or RH 8 and derivatives as we did not want
to rebuild our server and 20 + workstations.

We simply dropped back to SL 6.5 and updated it to 6.9.
This is nuts but RH 7, 8 up -> is untrustworthy.  Before you shoot the
messenger, just try it.

Tried to file an install problem with almaLinus users group.  Moderator
shot messenger - just like the Kids at Fedora.

Nice piece of code - that is put in production without test - compiles
with out errors - Done.

10 years of work and a lot of money spent and you get a garbage desktop,
and a Linux with a dangerous flaw.   IBM/RH should be proud of this
work.

Still lookign for a usable linux.

I think the position taken by the labs is wise and 100% correct in light
of the test results over the last 8 mo.
The only good part is the minimum install and the linux behind the desk
top is alive and well.  From a command line point of view it works -
just like my Convex running BSD 4.2 30 years ago!!!!

Larry Linder