While A520 doesn't support PCIe gen 4 to the GPU, it does allow gen 3 to all PCIe devices even those on the chipset bus which will be all the PCIe slots 'below' the GPU and secondary M.2 sockets. B450 allows only gen 2 to devices on the chipset bus, so things like secondary M.2 NVME's will only get gen 2 at 1/2 the data throughput. That's only an upside if you plan on using it, and the board has a secondary M.2/NVME and not many low-end B450's have one for that reason.
For a 3600 processor it doesn't matter but if ever the time comes to consider upgrading CPU's to Ryzen 5000 an A520 is a natural fit with fully tested BIOS's. B450 boards will only get BETA BIOS's and may see limited future updates, so if that's an issue for you it's something to consider.
If i dont plan to overclock at all, is the b450 still a better option?
The B450 board has a terrible VRM design, with no cooling on the FET's. It would be an equally terrible idea to overclock it anyway, and makes them functionally equivalent in that regard, in my opinion. So, opinion: I'd say no since the A520 has better 'future proofing'.
Also, you can STILL overclock memory using XMP on A520. That's a much better way to bump performance for Ryzen anyway.