M4 and 2TB bootable external NVMe with Sequoia 15.4 working fine . . . so far.
Recently there have been a number of threads concerning serious problems making bootable external drives and/or installing Sequoia 15.4 on them.
This caused me some concern as I contemplated purchasing a base M4 mini but everything went smoothly so it looks as though there is no widespread problem (touch wood/knock on wood).
I fired up the new mini and went through the "Welcome" process creating an account.
Then I plugged in a 2 TB Thunderbolt NVMe (APFS formatted) and installed Sequoia on it in under 30 minutes.
So if anyone still has doubts about the process, they need not worry.
There was one very weird thing . . . when I launched Safari, all my saved Bookmarks and Passwords were there even though they had not been put on the internal SSD. I am wondering whether my M2 was open at the time and somehow transferred them wirelessly to the M4? It's never happened before.
Note: When connecting the external to install Sequoia I used one of the outer Thunderbolt ports as apparently the middle one is the DFU port and can't be used for installations.
Mac mini, macOS 15.4