How much it will bottleneck? Impossible to grade that without knowing your games, your preferred detail level etc.
1080p for 120FPS is doable on the 3070, at most you will see some asset loading issue (decompression, data fetch-pass through). Unless you know what to look for, Id wager you would have no idea what causes the low performance.
Ryzen 4500 is a lower mid-tier CPU on the PCI-e 3.0 bus. No resizable BAR, no direct access anything. 3070 is for sure much better than a 1050, but dont get your hopes up for a miracle.