[Query] Improve poor Wi-Fi network in Mivan construction technology based homes

I've fiber broadband connection from local vendor and they've provided Digisol's XPON router. In the room immediate to where the router is placed with no obstruction except for a wall (the wall doesn't even have plywood because TV unit isn't constructed), I'm not getting excellent network reception, even if I sit while facing my back towards that direction causing my own body to further block the Wi-Fi network signal, the signal drops to such poor state that I get speed of around 2-3 Mbps on a 100 Mbps connection.

To solve this, I purchased TP-Link Archer AX10 router and simply connected it via LAN cable to Digisol router provided by the ISP. After doing all this, experience has improved but only by a tiny margin. This router is supposed to be very good in terms of everything yet I don't get satisfactory signal, speed and peace of mind. The improvement is so minor that it doesn't justify the extra price I paid for the router.

It just didn't make sense to me why this happened until I found that Mivan based construction is the culprit here. I'm sure others would be facing the same as in the society where I'm residing, everyone complains of the same and have got repeaters to eradicate the issue.

Please suggest if there's any setting or something that can help me out here. I do know that it's hard to tell without having a look at the place in-person but do let me know if there's any setting within the router which can help me out. It's frustrating that the issue isn't fully resolved despite spending so much on a good router. I even feel that ditching this Wi-Fi 6 router, I should've gone for TP-Link Archer C80 which has even better coverage.

As of now, I've created both 2.4 GHz and 5 GHz networks with the same name and devices connecting to 5 GHz network get 90%+ of the claimed speed but on 2.4 GHz, speeds are almost 60%+ with good signal. When I turned ON smart connect, it wasn't behaving ideally, so, created separate network for both the bands keeping the same name. I do want my devices to seamlessly connect to the network having better speed as I move around the house. Please pour in your suggestions, I'm pretty sure many would've faced this.