Well, my approach has always been the same, and I just did it when installing the latest version of Big Sur, V11.1, onto an APFS-formatted partition on my (new) Samsung T7 1 TB external SSD (two other partitions on it are formatted as HFS+):

1. On my late 2018 Mac Mini running the latest version of Catalina, downloaded the Big Sur full installation file. It of course wound up inside my Applications folder.
2. Copied that file to another location on my internal SSD, and then deleted the one inside the Applications folder. What that means, of course, is that by launching it from another location, it will not get deleted.
3. Attached the 1 TB Samsung SSD to a port (USB-C) on my late 2018 Mac Mini.
4. Navigate to the location of that V11.1 Installer file, launch it, and proceed to do a clean, fresh installation of Big Sur onto that partition on the external SSD.
5. As usual, am offered the opportunity to migrate files, folders, settings, etc. from either a Time Machine backup, another backup, or a Mac. I chose "a Mac", and pointed to my Mac Mini.
6. Everything proceeded flawlessly regarding that migration.
7. Finally, restarted my Mini from that external partition, and as expected, it worked.

The primary purpose for me doing this now is to test Big Sur, as three of my critical applications are not yet compatible with Big Sur. Been testing for 2 days, and so far, all is well.

In actuality, when I do make the final move from Catalina to Big Sur (most likely in January or February, and that depends on when Tech Tool Pro will have a version ready for Big Sur), steps 1 and 2 will be the same. Then, will proceed as follows:

3a. Attach one of my Samsung 850 Pro 512 gig SSDs (enclosed inside an Orico enclosure) to the respective machine (I have 2 Macs: the Mini, and an early 2017 Mac Book Air).
4a. Run Onyx (Catalina version) and Tech Tool Pro on the respective machine.
5a. Do a SuperDuper! backup to the applicable partition on the external SSD.
6a. Restart the Mac from that just completed SuperDuper! backup.
7a. Launch Disk Utility there and Erase and Format (as APFS) the internal SSD on the respective Mac.
8. From there, repeat steps 4 through 7 above, except of course I'd be restarting from the respective internal SSD.
9. Remove the Catalina version of Onyx, and install the Big Sur version (in case folks do not know, that came out on Monday, and works fine, as expected).
10. Finally, launch Tech Tool Pro, and create the eDrive.

All of that has always worked flawlessly for me, and I wind up with a clean, stable system.