PeteHski

I agree it is highly likely to be overly optimistic for a true 1 hour power, but if you are just using it as a simple benchmark reference to measure future gains then it doesn't really matter as long as you follow the exact same test procedure.
I don't think the OP actually mentioned what type of FTP test they actually did. It could have been a simple ramp test rather than a 20 min effort. Or even a 2x8. Again it doesn't really matter as long as they compare apples vs apples when re-testing at the end of the training block.

I also agree about setting some real life functional performance targets, but tracking your FTP is not a bad starting point while ramping up fitness. Initial gains with structured training are likely to be quite impressive and that should provide motivation. But sooner or later you require more tangible goals. My personal goals are based around completing various challenging events in a target time. I only test FTP and other performance metrics to set accurate power targets for structured training. As the OP is going to use Trainer Road then their ramp test FTP will be used as a basis to set interval power targets.