FWIW, there is a free software called GPSBabel that converts pretty much any GPS format to other GPS formats.
I still use MS Streets & Trips and translate the routes to .kml (Google maps) and my Chinese GPS is perfectly happy with it.
Tried that (and other tools) while ze GF still had her TomTom Rider 5, didn't work, the routing on the TT always differed largely from the original plotted in the Garmin utilities as the conversion deletes too many details...
(tried it also with the latest TT Rider 550, same skittish route results upon import, even when trying to mimic the original route on their MyTomTom online plotting tool, the resulted routing will vary widely, simply over the different navigation preferences of the device, and map materials in use...)
Far worse had the TTR5 that annoying RUT bug, means it
will not let you miss a start/shaping/routing point, and starts
insisting that you have to
make a U-turn back to it...

Completely useless when diverting due roadworks, stopping for fuel, having lunch, coffee or sightseeing...
It ended with me organizing a Zumo 220 for ze GF's NT700VA, which also suffers its genuine "Zumo-flaws" (like that entire series...

) but at least 'we're on the same page' while out riding
And of course had the Garmin product designers nothing better to do that to copy that BS in their latest Zumo and XT models...

If you get off the route for whatever reason they actually expect you to stop, open the properties of the active route and select [skip intermediate points] for a new entry...
But for editing the shaping/routing points one must first know their actual names/numbers... which are like "random"...
A befriended couple, he ST1300, she NC750X, has two Zumo 396, both running the same firmware installed, both have same the same mapset version installed, both get the same route, build on BaseCamp loaded on, and then both show different routes/results upon import... hilarious!!!...
And dare we've to divert from the planned route for any given reason... both have to stop, hectically punching their screens... pfffff...
That's why I prefer my +20 year old Garmin Quest-I (basically a miniaturized Street Pilot 3) so much...
When diverting from an active route it simply prompts "
Off Route! Recalculate? [YES]-[NO]"... on which you either can press [NO], or simply ignore, as the prompt goes away after 1 minute...
It just keeps plotting along, stubbornly, displaying your relative position to the original, magenta bearing-line on the screen...
And when you pull back into the route, it just keeps ticking along on like n.o.t.h.i.n.g. e.v.e.r. h.a.p.p.e.n.e.d. ... "...
in three kilometers bear right!... " ... acknowledged, thanx Hilde!...

It also doesn't care if you miss the actual starting point, doesn't matter if you enter your route a few hundred meters, one, or fife kilometers later... its too simple, plain and bare of any "fancy features" to act out...
And that's what I prefer... a navigation
assistant, absolutely reliable, unobtrusive, not distracting, calmly serving in the background...