Unfortunately, there is no good way to do this on D&D Beyond. DDB's search functionality is notoriously wretched, and the listing you found is the best that can be done for this specific problem using the tools at D&D Beyond. I did a manual inspection of that list, and it turns out that a significant majority of the creatures with the "legendary" tag on DDB also have the legendary resistance trait (86%). Rather than give you the full list of ones that do, I'll list the ones that don't...
40 out of 279 Legendary Creatures do not have Legendary Resistance.
- Aboleth
- Ancient Deep Crow
- Androsphinx
- Archon of Falling Stars
- Archon of the Triumverate
- Ashen Rider
- Atropal
- Beholder
- Bol'Bara
- Death Tyrant
- Diderius
- Drow Matron Mother (including Legacy)
- Drow Mother of Rebellion
- Enahnced Sphinx
- Fleecemane Lion
- Fungal Servant
- Githyanki supreme commander (Legacy only)
- Gorka Tharn
- Gynosphinx
- Hlam
- Juvenile Kraken
- Kraken
- Lorthuun
- Maegera the Dawn Titan
- Mordakhesh
- Mummy Lord
- Reduced Threat Aboleth
- Severin
- Solar
- Sphinx of Judgment
- Star Spawn Larva Mage
- Storm Giant Quintessent (Legacy only)
- Shaxalia
- Lord of blades
- Thessalhydra
- Thessalkraken
- Undying Councilor
- Unicorn
- Valin Sarnaster
- Warlord
Around 86% of legendary creatures do have legendary resistance, so the legendary filter in D&D Beyond is probably "good enough". There unfortunately does not appear to be any clear rule for which legendary creatures lack the resistance trait, even some of the lower-CR creatures have, while others do not. But 8.6 times out of 10 you'll get what you're looking for if you just pick one from the filtered list on D&D Beyond.