We looked into this in advance of our trip, too! Our reason was covid, but eating outside is just delightful anyway. We ended up biting the bullet and doing a few indoor ADRs, but we balanced them out with several outdoor meals. I found this resource very helpful:
https://www.disneyfoodblog.com/2020...-guide-to-all-outdoor-dining-at-disney-world/
Some of this is mentioned above, but just to summarize them in one place, what we found was:
DHS - no ADR-able dining, but walk-up Hollywood Brown Derby Lounge does, and uses some of the HBD menu (our wait for two people was 40 minutes)
Epcot - Rose & Crown, Spice Road Table, Via Napoli (we did Rose & Crown's patio... it's really nice; it even started to rain, but it's covered, and we were fine)
MK - only Tony's; you could also go to the monorail resorts and eat on a walkup basis at a lounge
DAK - none, but Nomad Lounge has plenty of outdoor seating and serves some of the same food as Tiffins (we did this; our wait for two people was only 10 minutes at a time when waits for four were 50)
Disney Springs - many! Rather than list them, I'm just going to point back to the top of the thread at the DFB link. We had an ADR for Wine Bar George, but unlike Rose & Crown, they did not have well-covered seating, so even though we got there
after it had rained and not during it, they still sat us inside. The other place we considered was Raglan Road. LOTS of outdoor tables there.
Basically, don't be afraid to try the lounges, even though you're at the mercy of the walkup waitlist. They are table-service, you just can't make an ADR for them.