slow boot from external drive

Is FileVault enabled? It’s turned on by default in Tahoe. Modern Macs have hardware-supported encryption/decryption for internal storage, but if your OS is on an external drive the decryption will be (relatively) much slower.

Another solution to your problem:

Is to run macOS and App's on the Mac mini's faster internal drive, then move your Doc's, Files and larger Photos, Music, Movie Libraries to an external drive.

Move your Photos library to save space on your Mac - Apple Support

Change where your music files are stored on Mac - Apple Support

Move your iMovie for Mac library - Apple Support

Free up storage space on Mac - Apple Support

What external drive are you using…?

What items are set to startup at login…?

What else have you tried besides reinstalling…?

Next time the external drive is slow, try Safe Mode followed by a Normal startup.

see > Start up your Mac in safe mode - Apple Support

The solution there is to buy a Mac with sufficient internal storage for your needs. IMO, it’s fine to store data externally but Macs are designed to run macOS on the internal drive.

Supported isn’t the same recommended. Apple ‘supports’ disabling security protections and allowing downloaded malware to be installed. Apple ‘supports’ pasting scripts into Terminal that are offered up by malicious websites. That doesn’t mean doing those things are good ideas.

The external drive can have a large impact on how an external booting system works in addition to any other drives that you may have connected. The performance can also be problematic when using DIY enclosure/SSD combos.

So, as @den.thed has asked, what external drive are you using.

iPhoneSE16Dream wrote:

I have Mac mini M4 with 16GB RAM and 256GB drive

Those machines are only suitable for kiosk-style applications where only a single app is ever running, such as a check-in station at a hospital or a directory lookup at an office building. The hard drive is simply too small for any other use.

etresoft wrote:

Those machines are only suitable for kiosk-style applications where only a single app is ever running, such as a check-in station at a hospital or a directory lookup at an office building. The hard drive is simply too small for any other use.

I think that’s a rather harsh characterization. Sure, I have 2 TB in my MBP and the other 5 Macs in the house have 512 GB (3) or 1 TB (2). But looking at the actual usage of my wife and kids’ Macs, they range from 65 GB to 200 GB, and they all have multiple apps installed (MS365, some have Photoshop CC, games, etc.), photos, etc.

I personally wouldn’t buy a Mac today with less than 512 GB, but I wouldn’t say 256 GB is going to be limiting for everyone. Especially with a desktop machine where a fast, multi-TB external SSD can be used for data storage.

iPhoneSE16Dream wrote:

256GB is not enough but that's beside the point as OS does offer the solution and work arounds such as installing large apps on external drive, move user home dir to external drive or even install OS on external drive , however it fails to live up to promise of delivering the solution.

Does it really promise that? There are perfectly valid and reasonable reasons to buy a 256 GB drive. But it's really not appropriate for most users.

iPhoneSE16Dream wrote:

Hi all, I have Mac mini M4 with 16GB RAM and 256GB drive, so I installed the OS on external drive

Typically, a much better strategy is to keep macOS and your applications on the internal storage, and attach external storage for data/files/etc.