Try the Windows 22H2 update, it has speeded my computer up.

Please let me know if there's a solution that I can try or if it's a known bug when it would be fixed.

I have turned off hardware acceleration / Open CL after seeing some other threads on similar (but not exactly same) lag issue - however it hasn't helped. (19044.2251) and face no such issue with Designer V1. I am using Designer V2 on Windows 10 V 21H2. It seems like the lag is slowly creeping in before becoming noticeable. I reminds me of some earlier version of Designer V1 that had similar lag (which version resolved it I don't remember now). The files I am working on are not that heavy, in fact most of them are under 1MB (it uses many gradients and vector brush) but still it lags severely. For example, the selection of any object, selection of a new tool from the toolbar by click or by keyboard shortcut, selection of a context menu button takes 3-5 sec or more!

When I use Designer V2 - it works fine for sometime (may be an hour or so - can't be exact on this) but then it starts slowing down and everything becomes really laggy.

Affinity designer v2