GPU
Just any eGPU case and any recent desktop AMD card will blow mbp away...
LOL, today that would cost a fortune. Are you remotely aware of the insanity of current AIB GPU card pricing?
I bought a Sapphire Pulse Radeon RX 580 card in June 2020 for $180, a fifty dollar markdown from the April 2017 launch price of $230. Fine. I didn't want to pony up another hundred bucks for the newer RX 5700 XT (especially because I needed to upgrade to Crapalina for GPU support).
Today that same RX 580 card is being offered by third-party sellers on Amazon for $750+. That over
4x the price I paid last summer.
Four.
Year.
Old.
Graphics.
Card.
Between the price of a Sonnet eGFX Breakaway Box and the street price of an RX 580, that's nearly $1100.
I also bought a Sapphire Pulse Radeon RX 550 2GB card for a productivity Windows PC build for $65 in October, $15 less than the $80 launch price (again from 2017). Today's street price for this card is again around 4x what it was six months ago. This is a low-end discrete GPU, the main benefit being that it uses little power (it doesn't even require a power cable from the power supply; it gets all of its power from the PCI connector).
Suggesting a discrete GPU + eGPU enclosure was a valid alternative six months ago. In early 2021? No, not really.
Remember that GeForce cards are not an option and only a subset of Radeon cards are supported by Apple. The ghetto $65 Lexa PRO RX 550 that lives happily in my Windows 10 SFF build is not supported in macOS.
If you're trying to get better graphical performance out of a Mac mini 2018, right now you're basically screwed unless you are willing to pay an arm and a leg for an overpriced legacy Radeon GPU.