If you fly for an airline its really simple: Look at your FOM and use that guidance.
At my employer, outside commercial flying was not allowed due to the prior time limits. It took a year, but the rules were eventually relaxed to match 117, and now I can go legitimately instruct or do other part 91 (non 91k) work in my free time if I want.
Same story at my company. They officially announced in late February that outside flight instruction was no longer considered commercial flying, making it officially permitted.
