Need help with PC upgrade

i think it' even better to use 4TB HDD as data in PC
and then also using NAS as backup

i rarely partition entire HDD except the first time using it
the only thing is, NAS are expensive lol

You motherboard supports several series:

Supports AMD AM4 Socket Ryzen™ 2000, 3000 and 5000 Series

I would only replace the motherboard if the new one had DDR5 support.

Probably - but your total RAM will run on the slowest RAM's speed.

Yes but its not ideal , timings will be off if its not the same brand and runs at the lower speed of the 2

Well the major thing you would want to do is upgrade to 32GB of 3200 RAM. You could go more, but anything beyond 3200 provides diminishing returns performance wise, 3200 is the sweet spot. You could go more than 32GB, go 64GB if you wish, but how much difference it would make in your workloads isn't something I can give accurate info on.

If you want an extra boost to your productivity, you could go for a 5000 series AMD. a 5600X would give a nice boost to both gaming and productivity over what you have, or if you really want to push that productivity to the limit, go for a 5950X, tho note it's gaming performance may be slightly less than the 5600X, though still better than the 3600. Your current motherboard will support 5000 series CPU's, so changing isn't a requirement, but it would require a BIOS update, assuming those have been rolled out already, I'm not sure, haven't been paying attention to that myself, you'd need to look into it.

Also adding in a good NVMe drive would be beneficial in some productivity tasks as well.

That all said though, your PC is pretty good. If I were in your position, at most I'd get a good NVMe, and upgrade my RAM to 32GB 3200, but beyond that I probably wouldn't bother with much, unless it's how you make money. If it is, then yes, get a 5950X, and maybe go 64GB for RAM. Otherwise, wait a generation or two and just build a new PC to really get the most for your money.

You're question confuses me...:
If you need more storage because your drives run full of data then you get a new drive.
RAM can help with tasks like video rendering (and I say 'can' on purpose instead of 'does'), emulators (not sure if they actually need more than your 16GB - you could check that while running them in the system resource monitor) or heavily modded games (while 16GB should still be more than enough for basically all the current games by themselves).
So the questions I'd ask would be: What do you actually need, where do you feel your system is insufficient OR how loose is your wallet and your urge to just get new 'toys'?

You know, we both got pretty similar setups (same CPU, similar MB, I got 2x16GB RAM sticks (2133MHz of four year old Kingston ValueRAM overclocked to 2666MHz with fast timings) and a RX5700, 500GB SSD for the System, 1000GB for software/games (because the 500 wasn't enough anymore for the system plus software/games), 4TB HDD for data, 4TB HDD for backups). I did a lot of video editing some years and am gaming e.g. CoD MW, CW or Warzone at 60-70fps on highest settings or at about 120 fps with competitive settings - and I don't feel like my system could benefit from any hardware update that would be worth the investment. Sure, 3200MHz or higher clocked RAM would be nice - would it be worth the investment? Hell no! Sure I'd like to have a new GPU - would that be worth the money and would it even bring any benefit at all for what I'm using it for? Absolutely not. Now... a high refresh rate monitor with free sync - that could be something fun. On the other hand my Dell U2515H is still superb and right now there's no monitor that I know of which offers everything I'd want for a price I'd be comfortable paying. But, what it comes down to if I'd be doing anything that you are doing with your system, I only might get my RAM up to 32GB and get more storage if the storage I have isn't enough for the projects (and for keeping backups of them).