These are the gold standard for heating a fastener while minimising damaging to the surroundings, except if there are delicate electronics nearby. The downside is, they are VERY expensive. Consider this option only if you are a pro or very active DIYer... or loaded!

SOLARY Flameless Handheld Induction Heater Kit | 1000W, 220V | Magnetic Tool with 3 Coils | Bolt Heater for Rusty Screws Removal
4.0

Solary Magnetic Induction Heater Kit, 1000W 220V Flameless Heat Tool for Bolt Removal, with 8 Coils and Tool Box
4.0