bow toe rail alternatives to varnish

For external teak (but not covering boards or decks) I give them a "hard candy shell" of epoxy topped with a UV LPU paint such as Alexseal, Awl Grip or Imron. I start by applying four or five coats of high-solids epoxy, (usually West 105/207). If that fills all the pinholes and grain, sand down with 180/220 grit then begin building up the clear. It may be overkill but I like to shoot five coats a day, sanding (220 grit) between each batch until the surface is fair and true, then sand a final time with 320 grit and shoot the final "money shot" after wiping down and tacking to get rid of dust.

It is more work initially to properly apply the necessary multiple coats but they'll last five years or more with no maintenance whatsoever. After five or so, the outer layer will start to lose it's gloss and you just lightly sand it off and apply another layer which resets the clock for another five years. This is the same method all the fighting chair manufacturers coat their creations.

can you put varnish over the epoxy?
I think so, but have never done it.
I know WestSystem will yellow with UV light if not covered.

I use two part varnish in the North East.
It seems to last 3-5 years uncovered.

I've had good luck with the Cetol marine teak color, 2 coats of that and 2-3 coats of clear cetol over it. That can easily be done at the dock. Also recently did a boat with the Awlgrip Awlwood and that went on nice and looks nice, but it was only done in November...... That too doesn't need as many coats as varnish

Yes you can "varnish" over epoxy. Most people use a synthetic varnish or 2 part poly varnish over the epoxy.

West does, or at least did, make an epoxy with UV filters in it.