Indeed, basso continuo parts for theorbo should be notated in the bass clef. Occasionally we will jump into the alto and treble clef range, but the bass clef is primarily what we use.
For solo theorbo repertoire, tablature notation is preferred. It has a significant advantage to modernized staff notation, owing to the double re-entrant tuning version of the instrument that the vast majority of the surviving music is written for. One of the primary reasons we prefer tablature is due to the Campanella Effect- the technique theorbo composers use which enables notes to sustain over each other on adjacent strings, creating a smooth legato effect. It is one of the outstanding and unique features of the instrument, but the problem is that the modern staff notation of this effect is highly illogical and difficult for the mind to process and the body to execute. Because tablature shows you where to put your fingers, instead of what the pitch value of the note is, it is much, much easier to execute these passages without disorienting the mind. For example, a hypothetical ascending scale using the Campanella technique will not go from the lowest numbered string on the instrument to the highest like one would expect on a conventionally tuned plucked stringed instrument. Instead, it might start on the 2nd string, then go up to the 1st, down to the 3rd string, back up to the 1st string, and finally back down to the 3rd string. Take note that the highest note of this hypothetical ascending scale is on the third string! It is important to realize just how illogical and unnatural this feels if you try to make it happen with modern notes that have guitar-like numbers for which string the note is played on. Tablature takes the guesswork out of it. You just put your fingers down where it says, keep them down, and the magical over-legato effect is produced. From this perspective, “archaic” tablature notation is actually an amazing and innovative technology that humanity had lost once the notation style fell out of popularity along with the instruments that used it.
This is why it is absolutely critical to have proper letter (and number) based lute tablature working as soon as possible in Dorico. With the auto-generation of tablature from modern notation, it would be easy to, for example, to take a modern staff notated scale run, and auto-generate the equivalent tablature notes required to execute it in the Campanella style. The math required to do this is not difficult, but we just need people to ask for these features in order for them to get promoted to a higher priority on the to-do list for this glorious software.
I am sure that this topic was covered in your workshop, but if you need any more info, please don’t hesitate to reach out. Examples can be provided if needed. The theorbo is a special instrument and we need more composers writing for it, so we’d like to assist if there are further questions.