BudsGunShop.com - Choke

William, it is removable and this package Includes: (1) AccuChoke Choke Tube: Modified. Cheers and stay safe!

TSS arms also says there are no additional chokes for this shotgun
https://tsswarehouse.com/shop/mossberg-maverick-88-field-20-gauge-pump-action-shotgun-26-barrel-blued-finish-mossberg-32201/

it comes with a mod accu-choke removable choke see ****** Manufacturer Maverick Arms
Pricing Unit GN
Model 88
UPC 049533322012
SKU 32201
Width 7.5000
Length 38.5000
Height 3.5000
Weight 8.5000
Action Pump
Action Type PUMP
Barrel Description Vent Rib
Barrel Finish Blued
Barrel Length 26"
Barrel Length In Inches 26.0000
Barrel Length Range 26" to 26.99"
Barrel Type Vent Rib
Caliber 20 Gauge
Capacity 5+1
Chamber 3"
Checkering N
*******Choke Configuration Accu-Choke
Choke/id Modified Only
******Chokes Included Modified
Dimension 2.70 X 8.20 X 36.60
Finish Blued
Finish/color Blue
Gauge 20 Gauge
Grip Type Mossy Oak
Hand Right

it comes with a mod accu-choke removable choke see ****** Manufacturer Maverick Arms
Pricing Unit GN
Model 88
UPC 049533322012
SKU 32201
Width 7.5000
Length 38.5000
Height 3.5000
Weight 8.5000
Action Pump
Action Type PUMP
Barrel Description Vent Rib
Barrel Finish Blued
Barrel Length 26"
Barrel Length In Inches 26.0000
Barrel Length Range 26" to 26.99"
Barrel Type Vent Rib
Caliber 20 Gauge
Capacity 5+1
Chamber 3"
Checkering N
*******Choke Configuration Accu-Choke
Choke/id Modified Only
******Chokes Included Modified
Dimension 2.70 X 8.20 X 36.60
Finish Blued
Finish/color Blue
Gauge 20 Gauge
Grip Type Mossy Oak
Hand Right

This shotgun has a fixed "modified" choke. And is not interchangeable.
Full specs here.
mossberg.com/product/maverick-88-all-purpose-32201/