Update 2: this happens only on nvidia gpu. When running on AMD iGPU everything works fine. I guess it's just nvidia being nvidia

Update: the smaller the window - the faster the resizing. Small windows (around 400x400px) are pretty fast to resize - still laggy, but not critical. When it gets bigger the more time it consumes. When I try to resize almost whole monitor-size picture (1920x1080) it can take up to 5 seconds

Takes ~2 seconds to resize image. App is completely frozen during this time. Using wayland session, kde plasma 5.27.5 and nvidia graphic card with latest proprietary driver. Forcing run imv-x11 works fine for resize, but zooming in/out a bit laggy too (ok for imv-wayland)