Is Mac Mini suitable for self-hosted server?

Using the igpu might be problematic for transcoding if you need that. I'd recommend older intel / Asus NUCs if you want a mini PC. 3 year warranty, built for Enterprise, tall version has room for a 7mm tall sata SSD or HDD along with nvme m.2 SSD.

I think if you do Asus 12gen + they have another m.2 slot though it is the smaller one 2242. Doing all this you can upgrade it to 64GB RAM, 8TB m.2 2280, 8TB SATA SSSD, and 1TB M.2 2242. In homelab especially with mini PCs the limit is usually RAM / storage rather than CPU.

I got 4 11th gen with 64 GB RAM each and 32TB of SSD storage. I recommend avoiding QLC SSD as much as possible. Aim for TLC , MLC, or SLC. Higher storage capacity tends to be QLC or TLC, QLC has shortest endurance and slowest speeds.