Poser may run on a Linux machine, and you will be able to compute using only the processor...

That being said: your PC will remain safe as long as it is not used to go to the Internet using browsers, emails, telegram, whatsapp and all that stuff.
I mean: if you setup a strong firewall with one thing going from inside to outside (Poser) and nothing in the other direction, you may run your PC till it physically dies. And there are enough strong free firewall, if you don't trust Windows' own one.

To access the internet, buy stuff for Poser, etc: use a newer, cheaper PC. 

Then to give access to what you just bought:
- either use an USB key
- or a NAS
- or your internal network, with one shared folder

I advice to rely on two firewalls:
- the one given by your internet provider
- a second one, that YOU control, such as Asus' excellent devices
That plus the PC's internal firewall and you'll be safe.
That's the configuration I've been using since the old times when we had to connect using modems. and it has a serious Plus: if you change your internet provider, nothing changes inside your own network.

And the advantage of a NAS, even if it may be expensive: no direct link between both PCs, no need to share any folder.
In my case, I made the jump for a RAID5 Synology.

𝒫𝒽𝓎𝓁

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(っ◔◡◔)っ

👿 Win11 on i9-13900K@5GHz, 64GB, RoG Strix B760F Gamng, Asus Tuf Gaming RTX 4070 OC Edition, 1 TB SSD, 6+4+8TB HD
👿 Mac Mini M2, Sonoma 14.6.1, 16GB, 500GB SSD
👿 Nas 10TB
👿 Poser 13 and soon 14 ❤️