Optimal or maximum speeds you only get when every thing matches:
- ISP speed.
- Router hardware.
- Client hardware.
- The environment, hardware locations and the distance between router and the wireless clients.
Your ISP is obvious, for a higher possible speed you need to pay more. Keep an eye on the below and watch out you are not subscribing to speeds that are by far not feasible for your situation.
The Wi-Fi hardware develops over the years, most common standards these days are 802.11ac / Wi-Fi 5 and 802.11ax / Wi-Fi6, newer standards are in general faster. For optimal results the router and clients shall be of the same standard.
With the Wi-Fi standard also the number of data streams / antenna's plays an important role: more data streams / antenna's means a higher speed, for optimal results the client shall have the same number of antenna's as the router. Usually clients are limited to one or two antenna's.
Depending on the environment (rural area versus a crowded apartment building), distance and disturbance, the router accepts certain settings. Most important is the bandwidth on 5 GHz, for the highest speed you need 160 MHz. Usually you only get 80 MHz which half's the capability.
This table indicates Wi-Fi standards and the maximum data rate per data stream for a given bandwidth for 5 GHz or 6 GHz (Wi-Fi 6E):
The above shows that the possible or final Wi-Fi speed is not a straightforward number, it is always the sum and result of many variables.
[EDIT]
And very right said by Yota, if speed is ultimately important: use a 1 Gbps wired connection from your PC to the router without the need to upgrade the router.