Umbrella issue for 26.0 testing. Please help testing on a wide variety of supported platforms, as well as interaction with different software.

Let us know which version you tested on which operating system.

If you find an issue, please search Github for known issues first and then open a new Github issue.

*This meta issue should not be used to report bugs, as a single thread makes it impossible to track more than one topic.*

See [26.0 Draft Release Notes](https://github.com/bitcoin-core/bitcoin-devwiki/wiki/26.0-Release-Notes-Draft) for a list of changes.

See here for the testing guide: https://github.com/bitcoin-core/bitcoin-devwiki/wiki/26.0-Release-Candidate-Testing-Guide.
*        │   │
 *        │   │
 *        │16 │
 *        └───┘
 *
 * Here m_free_lists[1] holds the 2 blocks of size 8 bytes, and m_free_lists[2]
 * holds the 3 blocks of size 16. The blocks came from the data stored in the
 * m_allocated_chunks list. Each chunk has bytes 262144. The last chunk has still
 * some memory available for the blocks, and when m_available_memory_it is at the
 * end, a new chunk will be allocated and added to the list.
 */
template <std::size_t MAX_BLOCK_SIZE_BYTES, std::size_t ALIGN_BYTES>
class PoolResource final
{
    static_assert(ALIGN_BYTES > 0, "ALIGN_BYTES must be nonzero");
    static_assert((ALIGN_BYTES & (ALIGN_BYTES - 1)) == 0, "ALIGN_BYTES must be a power of two");
    /**
     * In-place linked list of the allocations, used for the freelist.
     */
    struct ListNode {
        ListNode* m_next;
        explicit ListNode(ListNode* next) : m_next(next) {}
    };
    static_assert(std::is_trivially_destructible_v<ListNode>, "Make sure we don't need to manually call a destructor");
    /**
     * Internal alignment value. The larger of the requested ALIGN_BYTES and alignof(FreeList).
     */
    static constexpr std::size_t ELEM_ALIGN_BYTES = std::max(alignof(ListNode), ALIGN_BYTES);
    TES must be a power of two");
    static_assert(sizeof(ListNode) <= ELEM_ALIGN_BYTES, "Units of size ELEM_SIZE_ALIGN need to be able to store a ListNode");