I am thinking about buying 2 separate tickets for a connecting flight on Munich Airport - the first one operated by Lufthansa and the second by TAP Air Portugal, hence both belonging to Star Alliance and operating on Terminal 2 MUC. There is a 1h40 difference between the arrival of the first and the departure time of the second flights. Would you recommend buying them as a likely safe connection? The price of buying the 2 tickets separately is almost half of buying them on the same ticket... Thanks!
Without checked bags, this should be doable, though you'll have to go through immigration. Terminal 2 at MUC has a minimum connection time of just 30 minutes, so you have sufficient time if there aren't delays.
However, by arranging your own connection with two separate tickets, you are taking on the responsibility for delays yourself. If your first flight is delayed and you miss the Lisbon flight, the airline may well make you purchase a new ticket for a future flight at the full walk-up price, which could prove rather expensive. You'll also be responsible for your expenses if you have to stay overnight until the next flight.
Personally, I try to avoid separate tickets and leave substantially more time between flights when I book them, but this depends on your tolerance for risk and the potential savings/costs of the options.