20 cards where it’s legal in Commander and the color identity ≤ UW and the card types include “planeswalker” and ((the full Oracle text includes “gain” and the full Oracle text includes “life”) or the full Oracle text includes “lifelink”)

Ajani, Adversary of Tyrants (Core Set 2019 #3)
Ajani, Caller of the Pride (Foundations #134)
Ajani Goldmane (Magic 2011 #1)
Ajani, Inspiring Leader (Core Set 2020 #282)
Ajani Steadfast (Commander Masters #813)
Ajani, Strength of the Pride (Core Set 2020 #2)
Ajani, Wise Counselor (Core Set 2019 #281)
Archangel Elspeth (March of the Machine #6)
Dovin, Architect of Law (Ravnica Allegiance #265)
Dovin Baan (Kaladesh #179)
Dovin, Grand Arbiter (Crimson Vow Commander #153)
Elspeth Resplendent (Streets of New Capenna #11)
Elspeth, Sun's Nemesis (Theros Beyond Death #14)
Elspeth Tirel (Scars of Mirrodin #6)
Gideon Blackblade (Ravnica Remastered #20)
Teferi, Timebender (Dominaria #270)
Teferi, Who Slows the Sunset (Innistrad: Midnight Hunt #245)
The Wandering Emperor (Kamigawa: Neon Dynasty #42)
Ugin, the Spirit Dragon (Core Set 2021 #1)
Urza, Planeswalker (The Brothers' War #238b)

This search is finished. Now the real work can begin.