I tried FattyJoker's suggestion and the GlovePie suggestion for this. No luck.

When I was trying to get the game running on Win10 I came across Blood2StarterKit.7z. 9MB. It's on moddb. From what I can see it's the whole game with dgvoodoo and the WIDESCREEN.REZ, but doesn't include the game's 3 large files. BLOOD2.REZ, BLOOD2NM.REZ and SOUND.REZ. So I added those myself.

Changing the weapons with the wheel was working OK. Wanting to change the inventory previous/next, I accidentally changed weapons previous/next. That screwed changing weapons with the wheel. I will add that weapon change with the mouse wheel was selected in the menu.

So I just ended the game and grabbed the autoexec.cfg from Blood2StarterKit and started the game again and the mouse wheel worked again. Before I add the next bit I will add that I'm in the UK so it's a UK keyboard I'm using just in case it matters. So, it was then that I noticed that previous weapon is set to ; whilst next weapon is set to ' as well as mouse1, which is strange as Fire (weapon) is also set to mouse1. Hitting ; does work for previous weapon, but if I hit ' I get the game's console.

I decided not to play around any more to see what's going on. Maybe related to what HenitoKisou said about old mice?