since I already have a Mac for work I was wondering how suitable a Mac Mini M1/M2 would be for a homelab?

Suitable yes, if you want to do it... maybe or maybe not. Here's a few pointers:

• Debian can be installed on those machines, however I'm not sure how power management works properly:
• Installation isn't as straightforward and as easy as in another systems because Apple decided to keep pushing the usual ARM bullshit of not including a proper UEFI with the system;
• Some stuff will be broker, but you most likely don't need it for self-hosting;
• If you keep macOS around you may have good luck with virtualizing Debian using UTM or VMware. Debian's arm64 images will run at optimal performance on that hardware.

If you're about to spend money I would grab an HP Mini unit with a "T" CPU, those will downclock really hard and you can get a i5-10500T (on ebay) for around 250€... and everything will work fine out of the box. An i7-8500T model also sells for 150€ or something like that.

Have a look at those CPU benchmarks (last one is probably yours):

If you're looking for power efficiency the newer CPUs are always better. Those mini units will downclock and idle at around 9-12W depending on hardware configuration but Apple should be able to do better - at least assuming you've power management working.

https://www.cpubenchmark.net/compare/4104vs4922vs3768vs3231vs1287/Apple-M1-8-Core-3200-MHz-vs-Apple-M2-8-Core-3500-MHz-vs-Intel-i5-10500T-vs-Intel-i5-8500T-vs-Intel-Xeon-X3430

Got an M2 mini and at first had it running with MacOS and k3s (mini kubernetes). What annoyed me a bit was that if you restart you need to login to get kubernetes/docker starting up again. Also you cannot start docker desktop from cli, but need GUI access via apple remote desktop. You could remove the login but then your setup is completely unsecured against local access. After waiting a bit asahi linux supported the M2 mini and I gave it a try. It's a fedora linux, which I'm not super familiar with, but installing it was quite smooth and installing k3s was also easy and I'm only really using the server via ssh tunnel port forwarding and kubectl which is fine for me. It even uses less watt in this config what I remember after measuring. Restarting also starts k3s without login as with any linux. So quite happy with this config.

I don't recommend Debian for Apple Silicon, just stick with Asahi Linux. There aren't any big issues, except the fact that not all Docker images are built for arm64.

An m2 / m2 runs Debian?

The problem with Mac hardware is that it's ARM and vertically integrated with everything Apple. Not all hardware is supported by Linux because Apple won't write any linux drivers and everything is reverse engineered. You're better off buying something non-Apple which linux properly supports.

If power consumption is an issue for you get, a R9 7950X consumes as much and at times less power than an M1/M2 (I think even M3). Check out GamerNexus's charts. IINM AMD in W/Ghz performs better than Intel across the board.

No idea where you are, but you can get a small factor PC from one of the vendors that preload linux, or configure a small form factor PC of your liking for cheap and put linux on it. You'll get more out of your money for the same or better performance with about the same energy consumption (or a bit more).
Somebody I know who happens to live in Hungary got himself this cheap beauty. They deliver all over Europe, but if you live elsewhere on this planet, there probably is something similar like this out there.

Anti Commercial-AI license

I have a Mac mini m1 and run several containers to manage media, arrs and vpn. I also have a Debian vm for homeassitant. I had used UTM prior but now moved the vm to VMware fusion.

Main issue I run into is not enough ram as the base model only has 8gb. And I do not have redundancy optimised when I reboot. I have it locked with a password so it doesn’t auto run the containers or the vm.

I double the mac for light browsing too. I considered getting a dedicated Linux mini pc for the services next to a desktop Mac. But my usage is too sparse at both ends of the spectrum.

Everyone else has described the complications that a Mac mini would have. So why not consider something else? Lenovo, HP, and Dell make 1l ultra small form factor PCs and they're pretty cheap on eBay. They're also low power. Search for Tiny Mini Micro to find information.

I have three Lenovo Thinkcentre machines - two with 32gb RAM and one with 64gb RAM - running my Proxmox VE cluster. Highly recommend using those small machines instead of a Mac mini.

I have an old mac mini running nextcloud on Ubuntu, I did upgrade memory and plug in external ssd