ASUS PRIME B550M-K, AMD B550 (Ryzen AM4) micro ATX motherboard with 4x DIMM, dual M.2, USB 3.2 Gen 2 Type-A - £82.28 @ Amazon

Good price for an Asus B550 with 4 memory slots and 2 m2 slots. Also available for a few pennies less from another seller.

• AMD AM4 Socket for AMD Ryzen™ 5000 Series/ 5000 G-Series/ 4000 G-Series/ 3000 Series Desktop Processors
• 4 x DIMM, Max. 128GB, DDR4 4866(O.C)/4800(O.C.)/4600(O.C)/4466(O.C.)/4400(O.C)/4333(O.C.)/4266(O.C.)/4200(O.C.)/4133(O.C.)/4000(O.C.)/3866(O.C.)/3733(O.C.)/3600(O.C.)/3466(O.C.)/3400(O.C.)/3333(O.C.)/3200/3000/2933/2800/2666/2400/2133 MHz Un-buffered Memory
• HDMI 2.1(4K@60HZ)
• Total supports 2 x M.2 slot(s) and 4 x SATA 6Gb/s ports
• mATX Form Factor
• 9.6 inch x 9.6 inch ( 24.4 cm x 24.4 cm )

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Info added by @Sashecuador

ASUS is one of Fortune magazine’s World’s Most Admired Companies and is one of the top motherboard and gaming brands as well as a top-three consumer notebook vendor. ASUS is driven by passion and innovation and dedicated to creating quality products for a future smart life, designing and manufacturing products that perfectly meet the needs of today's digital home, office and person. Our wide portfolio includes MG248Q, Chromebox and a range of devices and components, along with AR and VR

AMD B550 (Ryzen AM4) micro ATX motherboard with dual M.2, PCIe 4.0, 1 Gb Ethernet, HDMI/D-Sub/DVI, SATA 6 Gbps, USB 3.2 Gen 2 Type-A

AMD AM4 socket: Ready for 3rd Gen AMD Ryzen processors
Comprehensive cooling: PCH heatsink and Fan Xpert 2+
Ultrafast connectivity: Dual M.2, PCIe 4.0, 1 Gb Ethernet, USB 3.2 Gen 2 Type-A
5X Protection III: Multiple hardware safeguards for all-around system protection
Cooler by Design
Prime B550M-K is engineered with an array of hybrid fan headers and features comprehensive cooling controls that are configurable via Fan Xpert 2+ software or via the UEFI BIOS, ensuring your rig stays cool and stable under intense workloads.

Multiple Temperature Sources
Smart Protection
4-Pin PWM/DC Fan

PCIe 4.0 M.2 (up to 64 Gbps)
PCIe 4.0 M.2 Slot supports up to 22110 and provide NVMe SSD RAID support for an incredible performance boost. Create a RAID configuration with up to PCIe 4.0 storage device to enjoy the fastest data-transfer speeds on the 3rd Generation AMD Ryzen platform.

USB 3.2 Gen 2 Type-A
Numerous USB ports support high-end rigs loaded with peripherals, including a rear-panel USB Type-A connectors with fast USB 3.2 Gen 2 connectivity for compatible cases.

SafeSlot Core
SafeSlot Core is the ASUS-exclusive PCIe slot. Featuring a fortified design that's anchored to the motherboard by a special hook, SafeSlot Core provides 1.6x stronger retention and 1.3x greater shearing resistance than standard expansion slots.

ASUS Prime motherboards have strengthened solder points around both the PCIe and DIMM pins.
Overvoltage Protection
An exclusive circuit design with built-in voltage regulators to protect your motherboard from damage caused by unexpected high-level voltages from unstable or inferior power supplies.
LANGuard
ASUS LANGuard is a hardware-level network protection feature that integrates advanced signal-coupling technology and premium anti-EMI surface-mounted capacitors to improve throughput and ensure a more reliable connection.