5g may not be available in your area yet - we are a couple of years away from having decent 5G coverage in all metro areas. To date there are limited releases in a handful of suburbs by Telstra and Optus. 5g has all the challenges that a Fixed Wireless connection has wrt line of sight to tower, building penetration etc, recent article stated that those who have 5G right now are rarely getting better performance than 4G.
If you are in a FTTP coverage area (you have won the nbn lottery), Id go for that with a RSP who doesn't require you to get a contract , then you can reassess when 5G is more mature and confirmed to be available in your area. From pure technology pov 5G is not ever going to be faster than Fibre, as the 5G towers are connected by fibre themselves.
The only limitation on FTTP is the speed tier you choose to purchase and the quality (or lack there of) the RSP/ISP you choose to go with, a poor RSP will not buy sufficient cvc which can impact performance in peak times.
For high volume usage a fixed line connection will always be cheaper than mobile.