XTech Tactical has been in the business of magazine extensions, magazines, and pistol grips since 2013. Their magazine extensions currently cover the Smith & Wesson M&P line and the HK V9/SK pistols. XTech also makes a +3 extension for the Sig Sauer P365. New for 2023 is their +0 extension for the 365.
If you have meaty hands, getting a full firing grip on the Sig Sauer P365 can be impossible when using flush-fitting 10-round magazines. The +0 extension adds no additional capacity, which makes it legal to use in ban states, but you get a taller baseplate for your ring finger and pinky to fully grip the pistol. The extension also allows you to gain the shootability of the XL frame without having to make that additional purchase. Because there is no change in the inner dimensions of the magazine to increase capacity, you can use the factory springs and followers your magazines already use.
If you change your mind about having a +0 extension or laws change, XTech offers the extended spring, magazine spring button, and follower to convert your extension to +3 for a total of 13 rounds on tap.
The XTech Tactical P365 +0 extension can be had as a single unit priced at $14.95, but it may be worthwhile to pick up a pack of two for $24.95. The development for a +0 extension for the P365 in .380 ACP and P365 9mm Luger 12-round factory magazines is ongoing.