If you want a proper server, it seems that Asrock Rack is the only manufacturer of AM4-socket-based server mainboards. Unlike desktop/gamer boards, these are designed for parallel airflow, typically from front to back in a 19" rack. These also come with IPMI remote maintenance, so can be operated headless in a remote location.

I have considered one of these for a while, such as the X570D4U, which also supports up to 128 GB of ECC RAM. Depending on what you want, this may be overkill, though.

(This was my favourite, because it has two M.2 slots, but there are others with only a single slot, since you said you only need one.)

Unlike gamer or other boards, these have no fancy black vanity covers and often won’t allow overclocking, but are typically very well designed and rock solid for unattended 24/7 operation.

Not so much server-based, but the experimental part of “lab” is well covered: I replaced my late-2013 27" iMac’s internal HDD with an SSD. It’s a really delicate procedure, as the display is glued to the chassis; it needs to be cut loose and very carefully removed (it’s tempered glass), and then re-glued with special adhesive strips. But the performance gain is worth it. In addition, it also now runs Ventura, even with the nVIDIA card, thanks to OpenCore Legacy Patcher. Feels like a new machine now, and is perfectly adequate even for small video editing tasks with its 32 GB RAM.