Quite a lot of good riding to be had from the North end of the lake with two caveats:
1) The Gardesana tunnels. A bigger issue on the Western side but manageable even if annoying. Bring some lights. They are constructing a bike path right now on the outside of the cliff face directly over the water but it is available only in fragments up to now and you have to share it with lots of pedestrians, when I went from Tremosine up to Riva during the Alpi4000 in July 2018 I gave it a miss.
2) The only tarmac road from Lake Ledro down to Riva leads through a long tunnel officially closed to cyclists. It is a constant downhill and I went through there once (again with lights) and it was not a problem technically as the cars will only be marginally faster than you. Transit takes about five to seven minutes. But I have heard rumors of Carabinieri controls and fined riders.
Apart from that there are plenty of rides with spectacular roads and views, even though many tours will be longer than the range you indicated. And Lake Garda is crowded during the season so you will definitely not be on your own, ever. Weekend traffic around the Southern end can be downright horrific:
- Riva, up the Sarca valley past Arco and Dro, past Lago di Cavedine to Sarche and Ponte Arche (spectacular bike path through the gorge around the road tunnel), back via Passo Ballino and Tenno down a fabulous descent to Riva.
- Riva to Arco and Massone up Monte Velo, over Passo Santa Barbara down to Loppio and back over the hump to Nago and Torbole.
- Riva to Massone and again over Passo Santa Barbara but turn left at the junction, over Passo Bordala and past Lago di Cei up to Monte Bondone and down via Cavedine and back to Riva through the Sarca valley.
- Riva to Torbole, down the Gardesana Orientale through Malcesine to Torri del Benaco and then hop onto the Toscolano ferry (important means of transportation for cyclists). There, head North to Gargnano. In Gargnano you have two choices: Along the lake through the first tunnels to the Tignale turn off, up to Tignale and over the mountain to Tremosine, down to Limone and again through the tunnels to Riva. Or, turn left uphill in Gargnano and through the fantastic Valvestino to Lake Idro, North to Storo, on the Lake Ledro over the Ampola pass and down through the forbidden tunnel to Riva. I do not know how the Airnimal is off road as just before you enter the tunnel there is the turn off to the old Ponale road that was used before the tunnel was built but which has been downgraded to hiker and mountain bike use and is half gravel (but with really great views).
- From Riva down the Gardesana Occidentale tunnels past Limone to the Strada della Forra through the Brasa gorge up to Tremosine and on to either Limone or Tignale.
- Riva to Torri del Benaco and on to Garda, there turn East over the ridge, through Caprino Veronese up to Spiazzi and further up to Monte Baldo. Do the wild descent down to Mori and again via Loppio to Torbole.
Depending on your range and willingness to employ a car there is a lot more still. A circumnavigation of the lake is about 150km but I have only done that the weekends before Christmas yet when traffic is low.
If interested I can provide you with GPS tracks of the Rando Imperator, Verona-Resia-Verona, Solstizio d'Inverno and the Alpi4000 but you should also be able to find lots of those on Openrunner, too.