No need to feel embarrassed; things clicking into place that had never previously occurred is a core part of enjoying electronics!
Do you have a budget for programming tools? The ATMEL ICE programmer (needed for SAMD series) can seem like a bit of an investment. Whereas ST chips can be programmed by ST Links, either available as a sub-system on a dev board or a standalone (and clones are very cheap).
If a USB peripheral is a must have, then choices are pretty much as you’ve covered (although Raspi RP2040 may be worth a look too). If you can get your dopamine hit from other aspects of blinking, there are tonnes of options. I really like the new Microchip ATtiny 0 and 1 series chips. They are supported in the Arduino IDE but with a load of “baremetal” selectable options (check out the support repo). You don’t need external crystals (a single decoupling cap will do) and they run 10MHz at 3.3V+ or 20MHz at 4.5V+ ('cos they’re 5V tolerant and run down to 1.8V, so perfect for a pair of AA or a single lithium cell - I often use them with supercaps and photovoltaics!). They have some great little peripherals like the Event System (think simple interrupts that don’t even need CPU to process an ISR), custom configurable logic (logic gates), ability to measure their own supply voltage without external components, fast IO read and writes, low power 32kHz timer. They also come in hand-solderable SOIC packages or VQFN for more of a challenge (and more IO). Also, if you write code for them that you like, much of it is easily ported to the newer ATMEGA chips like the ATMEGA4809 that is in one of the newer Arduinos, as well as the AVRnnDX series that run faster (32 MHz). You can program an ATtiny 0 or 1 series chip (as well as ATMEGA4809 etc) with an Arduino Nano (or clone, running jtag2updi sketch) and a resistor, so that’s a pretty low bar to entry.
Sorry if that sounded like a hard sell but for playing around, they are great fun. For more ideas about what you can do with them, check out David Johnson-Davies’ blog where he has several interesting posts about them.