Apple has stated back in 2020 that this will be a 2-year transition, so the 'pro' Apple Silicon might not arrive for another year.
Thunderbolt 2 eGPU use isn't natively supported by Apple, but it can be enabled by open-source 3rd party software. There is some additional performance lost with TB2 vs TB3 and it is more of an amateur than a professional solution but it generally works.
EGPU Suggestions
A) Sonnet Breakaway Puck 5500XT. This is an all-in-one integrated eGFX/GPU box. These aren't much faster than a D500 or an M1 and can't easily be upgraded but are small and inexpensive... or at least slightly cheaper than just buying an M1 Mini.
B) Sonnet Breakaway Box. I use one of these with a 2018 Mini. Solid simplicity, but the blue LED lighting isn't for everyone. BYO GPU. If you have to stay on Catalina.... maybe an RX 5600XT?
C) AkiTio Node Titan. A bit more professional and travel friendly than the Sonnet, now sold by OWC. Radeon Pro W5700 bundles are available, otherwise BYO GPU.
More reliable alternative suggestions:
D) Get an M1 mini or Air as a stop-gap for the Redshift work while waiting for the next generation Apple Silicon.
E) 2019 Mac Pro (or a 2020 top-tier 5K iMac if budget is a factor).